Form N-Q

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, DC 20549

FORM N-Q


QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED MANAGEMENT INVESTMENT COMPANY

Investment Company Act file number         811-6548         

        Nuveen Select Tax-Free Income Portfolio         
(Exact name of registrant as specified in charter)


        333 West Wacker Drive, Chicago, Illinois 60606         
(Address of principal executive offices) (Zip code)


Jessica R. Droeger—Vice President and Secretary
        333 West Wacker Drive, Chicago, Illinois 60606         
(Name and address of agent for service)

Registrant's telephone number, including area code:         312-917-7700        

Date of fiscal year end:            3/31          

Date of reporting period:         6/30/06         

Form N-Q is to be used by management investment companies, other than small business investment companies registered on Form N-5 (§§ 239.24 and 274.5 of this chapter), to file reports with the Commission, not later than 60 days after the close of the first and third fiscal quarters, pursuant to rule 30b1-5 under the Investment Company Act of 1940 (17 CFR 270.30b1-5). The Commission may use the information provided on Form N-Q in its regulatory, disclosure review, inspection, and policymaking roles.

A registrant is required to disclose the information specified by Form N-Q, and the Commission will make this information public. A registrant is not required to respond to the collection of information contained in Form N-Q unless the Form displays a currently valid Office of Management and Budget (“OMB”) control number. Please direct comments concerning the accuracy of the information collection burden estimate and any suggestions for reducing the burden to the Secretary, Securities and Exchange Commission, 450 Fifth Street, NW, Washington, DC 20549-0609. The OMB has reviewed this collection of information under the clearance requirements of 44 U.S.C. § 3507.

Item 1. Schedule of Investments

    Portfolio of Investments (Unaudited)             
    Nuveen Select Tax-Free Income Portfolio (NXP)             
    June 30, 2006             
Principal        Optional Call         
Amount (000)    Description    Provisions (1)    Ratings (2)    Value 
    Alaska – 1.1%             
$          2,475    Alaska Municipal Bond Bank Authority, General Obligation Bonds, Series 2003E, 5.250%,    12/13 at 100.00    AAA   $   2,611,670 
     12/01/23 – MBIA Insured             
    California – 4.7%             
2,000    Alameda Corridor Transportation Authority, California, Subordinate Lien Revenue Bonds, Series    10/17 at 100.00    AAA    1,518,060 
     2004A, 0.000%, 10/01/25 – AMBAC Insured             
3,325    California Department of Water Resources, Power Supply Revenue Bonds, Series 2002A,    5/12 at 101.00    A2    3,683,269 
     6.000%, 5/01/14             
200    Contra Costa County, California, Certificates of Participation Refunding, Merrithew Memorial    11/07 at 102.00    AAA    207,498 
     Hospital Replacement, Series 1997, 5.375%, 11/01/17 – MBIA Insured             
3,000    Golden State Tobacco Securitization Corporation, California, Tobacco Settlement Asset-Backed    6/13 at 100.00    BBB    3,360,510 
     Bonds, Series 2003A-1, 6.750%, 6/01/39             
1,130    Los Angeles Department of Water and Power, California, Waterworks Revenue Refunding Bonds,    7/11 at 100.00    AAA    1,148,871 
     Series 2001A, 5.125%, 7/01/41 – FGIC Insured             
365    Los Angeles, California, Parking System Revenue Bonds, Series 1999A, 5.250%, 5/01/29 –    5/09 at 101.00    AAA    375,819 
     AMBAC Insured             
750    Tobacco Securitization Authority of Northern California, Tobacco Settlement Asset-Backed    6/15 at 100.00    BBB    756,540 
     Bonds, Series 2005A-1, 5.500%, 6/01/45             
10,770    Total California            11,050,567 
    Colorado – 13.2%             
1,300    Colorado Health Facilities Authority, Revenue Bonds, Catholic Health Initiatives, Series    3/12 at 100.00    AA    1,370,642 
     2002A, 5.500%, 3/01/22             
1,700    Colorado Health Facilities Authority, Revenue Bonds, Catholic Health Initiatives, Series    3/12 at 100.00    AA (3)    1,819,204 
     2002A, 5.500%, 3/01/22 (ETM)             
1,000    Colorado Water Resources and Power Development Authority, Small Water Resources Revenue Bonds,    11/10 at 100.00    AAA    1,069,630 
     Series 2000A, 5.800%, 11/01/20 – FGIC Insured             
10,750    Denver City and County, Colorado, Airport System Revenue Bonds, Series 1991D, 7.750%, 11/15/13    No Opt. Call    A    12,035,375 
     (Alternative Minimum Tax)             
640    Denver City and County, Colorado, Airport System Revenue Bonds, Series 1996A, 5.500%,    11/06 at 101.00    AAA    649,645 
     11/15/25 – MBIA Insured             
230    Denver City and County, Colorado, Airport System Revenue Bonds, Series 1996D, 5.500%,    11/06 at 101.00    AAA    233,466 
     11/15/25 – MBIA Insured             
5,000    Denver City and County, Colorado, Airport System Revenue Refunding Bonds, Series 2001A,    11/11 at 100.00    AAA    5,283,950 
     5.625%, 11/15/17 – FGIC Insured (Alternative Minimum Tax)             
    Denver Convention Center Hotel Authority, Colorado, Senior Revenue Bonds, Convention Center             
    Hotel, Series 2003A:             
1,000     5.000%, 12/01/22 (Pre-refunded 12/01/13) – XLCA Insured    12/13 at 100.00    AAA    1,051,940 
3,000     5.000%, 12/01/23 (Pre-refunded 12/01/13) – XLCA Insured    12/13 at 100.00    AAA    3,155,820 
5,000    E-470 Public Highway Authority, Colorado, Senior Revenue Bonds, Series 2000B, 0.000%, 9/01/28    9/10 at 31.42    AAA    1,324,250 
     (Pre-refunded 9/01/10) – MBIA Insured             
3,160    Northwest Parkway Public Highway Authority, Colorado, Revenue Bonds, Senior Series 2001A,    6/11 at 102.00    AAA    3,391,596 
     5.500%, 6/15/20 – AMBAC Insured             
32,780    Total Colorado            31,385,518 
    District of Columbia – 0.5%             
1,000    District of Columbia, Hospital Revenue Refunding Bonds, Medlantic Healthcare Group, Series    8/06 at 102.00    AAA    1,022,130 
     1996A, 5.750%, 8/15/16 – MBIA Insured (ETM)             
265    District of Columbia, Revenue Bonds, Catholic University of America, Series 1999, 5.625%,    10/09 at 101.00    AAA    278,997 
     10/01/29 – AMBAC Insured             
1,265    Total District of Columbia            1,301,127 
    Florida – 4.6%             
450    Escambia County, Florida, Pollution Control Revenue Bonds, Champion International Corporation,    12/06 at 100.00    BBB    453,042 
     Series 1993, 5.875%, 6/01/22 (Alternative Minimum Tax)             
10,000    JEA St. John’s River Power Park System, Florida, Revenue Refunding Bonds, Issue 2, Series    10/11 at 100.00    Aa2    10,334,800 
     2002-17, 5.000%, 10/01/17             
10,450    Total Florida            10,787,842 
    Hawaii – 0.6%             
1,330    Hawaii, Certificates of Participation, Kapolei State Office Building, Series 1998A, 5.000%,    11/08 at 101.00    AAA    1,363,942 
     5/01/17 – AMBAC Insured             
    Illinois – 14.0%             
1,965    Board of Trustees of Southern Illinois University, Housing and Auxiliary Facilities System    No Opt. Call    AAA    1,009,774 
     Revenue Bonds, Series 1999A, 0.000%, 4/01/20 – MBIA Insured             
    Chicago Heights, Illinois, General Obligation Corporate Purpose Bonds, Series 1993:             
3,820     5.650%, 12/01/15 – FGIC Insured    12/08 at 100.00    AAA    3,957,787 
2,600     5.650%, 12/01/17 – FGIC Insured    12/08 at 100.00    AAA    2,695,290 
195    DuPage County Community School District 200, Wheaton, Illinois, General Obligation Bonds,    11/13 at 100.00    Aaa    205,148 
     Series 2003B, 5.250%, 11/01/20 – FSA Insured             
805    DuPage County Community School District 200, Wheaton, Illinois, General Obligation Bonds,    11/13 at 100.00    Aaa    861,414 
     Series 2003B, 5.250%, 11/01/20 (Pre-refunded 11/01/13) – FSA Insured             
1,000    Illinois Educational Facilities Authority, Revenue Bonds, Midwestern University, Series 1998B,    5/08 at 101.00    A    1,021,100 
     5.500%, 5/15/18 – ACA Insured             
600    Illinois Educational Facilities Authority, Student Housing Revenue Bonds, Educational    5/12 at 101.00    Baa3    641,562 
     Advancement Foundation Fund, University Center Project, Series 2002, 6.000%, 5/01/22             
4,000    Illinois Finance Authority, Revenue Bonds, Northwestern Memorial Hospital, Series 2004A,    8/14 at 100.00    AA+    4,182,200 
     5.500%, 8/15/43             
1,320    Illinois Health Facilities Authority, Revenue Bonds, Decatur Memorial Hospital, Series 2001,    10/11 at 100.00    A    1,372,760 
     5.600%, 10/01/16             
2,700    Illinois Health Facilities Authority, Revenue Bonds, Lake Forest Hospital, Series 2002A,    7/12 at 100.00    A–    2,878,821 
     6.000%, 7/01/17             
300    Illinois Health Facilities Authority, Revenue Bonds, Rush-Presbyterian St. Luke’s Medical    11/06 at 100.00    AAA    300,270 
     Center Obligated Group, Series 1993, 5.250%, 11/15/20 – MBIA Insured             
2,275    Illinois Health Facilities Authority, Revenue Refunding Bonds, Elmhurst Memorial Healthcare,    1/13 at 100.00    A2    2,473,926 
     Series 2002, 6.250%, 1/01/17             
1,075    Illinois Health Facilities Authority, Revenue Refunding Bonds, Evangelical Hospitals    No Opt. Call    N/R (3)    1,109,755 
     Corporation, Series 1992B, 6.500%, 4/15/09 (ETM)             
3,125    Metropolitan Pier and Exposition Authority, Illinois, Revenue Bonds, McCormick Place Expansion    No Opt. Call    AAA    1,876,250 
     Project, Series 1992A, 0.000%, 6/15/17 – FGIC Insured             
500    Metropolitan Pier and Exposition Authority, Illinois, Revenue Bonds, McCormick Place Expansion    No Opt. Call    AAA    151,370 
     Project, Series 2002A, 0.000%, 6/15/30 – MBIA Insured             
5,000    Metropolitan Pier and Exposition Authority, Illinois, Revenue Refunding Bonds, McCormick Place    6/12 at 101.00    AAA    5,150,850 
     Expansion Project, Series 2002B, 5.000%, 6/15/21 – MBIA Insured             
1,300    Schaumburg, Illinois, General Obligation Bonds, Series 2004B, 5.250%, 12/01/34 – FGIC Insured    12/14 at 100.00    AAA    1,352,403 
    Yorkville, Illinois, General Obligation Debt Certificates, Series 2003:             
1,000     5.000%, 12/15/19 – RAAI Insured    12/11 at 100.00    AA    1,014,510 
1,000     5.000%, 12/15/20 – RAAI Insured    12/11 at 100.00    AA    1,012,110 
34,580    Total Illinois            33,267,300 
    Indiana – 8.3%             
5,000    Duneland School Building Corporation, Indiana, First Mortgage Refunding Bonds, Series 1999,    2/09 at 101.00    AAA    5,165,900 
     5.125%, 2/01/18 – MBIA Insured             
1,000    Franklin Community Multi-School Building Corporation, Marion County, Indiana, First Mortgage    7/14 at 100.00    AAA    1,027,630 
     Revenue Bonds, Series 2004, 5.000%, 7/15/22 – FGIC Insured             
2,000    Indiana Health Facility Financing Authority, Hospital Revenue Refunding Bonds, Columbus    No Opt. Call    AAA    2,294,800 
     Regional Hospital, Series 1993, 7.000%, 8/15/15 – FSA Insured             
9,855    Indianapolis Local Public Improvement Bond Bank, Indiana, Waterworks Project, Series 2002A,    7/12 at 100.00    AAA    10,438,810 
     5.125%, 7/01/21 (Pre-refunded 7/01/12) – MBIA Insured             
750    West Clark 2000 School Building Corporation, Clark County, Indiana, First Mortgage Bonds,    1/15 at 100.00    AAA    771,780 
     Series 2005, 5.000%, 7/15/22 – MBIA Insured             
18,605    Total Indiana            19,698,920 
    Kansas – 0.3%             
750    Wamego, Kansas, Pollution Control Revenue Bonds, Kansas Gas and Electric Company, Series 2004,    6/14 at 100.00    AAA    780,495 
     5.300%, 6/01/31 – MBIA Insured             
    Kentucky – 0.5%             
1,100    Jefferson County, Kentucky, Health System Revenue Bonds, Alliant Health System Inc., Series    10/08 at 101.00    AAA    1,129,326 
     1998, 5.125%, 10/01/18 – MBIA Insured (ETM)             
    Louisiana – 0.4%             
1,000    Tobacco Settlement Financing Corporation, Louisiana, Tobacco Settlement Asset-Backed Bonds,    5/11 at 101.00    BBB    1,046,750 
     Series 2001B, 5.875%, 5/15/39             
    Massachusetts – 0.9%             
500    Massachusetts Health and Educational Facilities Authority, Revenue Bonds, Partners HealthCare    7/11 at 101.00    AA–    542,995 
     System Inc., Series 2001C, 6.000%, 7/01/17             
1,055    Massachusetts Turnpike Authority, Metropolitan Highway System Revenue Bonds, Senior Series    1/07 at 102.00    AAA    1,061,647 
     1997A, 5.000%, 1/01/37 – MBIA Insured             
410    Massachusetts Turnpike Authority, Metropolitan Highway System Revenue Bonds, Subordinate    1/09 at 101.00    AAA    412,222 
     Series 1999A, 5.000%, 1/01/39 – AMBAC Insured             
1,965    Total Massachusetts            2,016,864 
    Michigan – 1.7%             
1,000    Michigan State Hospital Finance Authority, Hospital Revenue Bonds, Detroit Medical Center    8/08 at 101.00    BB–    959,800 
     Obligated Group, Series 1998A, 5.125%, 8/15/18             
2,900    Michigan State Hospital Finance Authority, Hospital Revenue Refunding Bonds, Trinity Health    12/12 at 100.00    AA–    3,004,835 
     Credit Group, Series 2002C, 5.375%, 12/01/30             
3,900    Total Michigan            3,964,635 
    Minnesota – 0.2%             
325    Minnesota Housing Finance Agency, Single Family Mortgage Revenue Bonds, Series 1995A,    7/08 at 101.00    AA+    327,649 
     5.200%, 1/01/17             
    Mississippi – 1.6%             
3,600    Calhoun County, Mississippi, Solid Waste Disposal Revenue Bonds, Weyerhauser Company Project,    4/07 at 103.00    BBB    3,764,628 
     Series 1992, 6.875%, 4/01/16 (Alternative Minimum Tax)             
    Missouri – 0.6%             
5,000    Kansas City Municipal Assistance Corporation, Missouri, Leasehold Revenue Bonds, Series    No Opt. Call    AAA    1,508,750 
     2004B-1, 0.000%, 4/15/30 – AMBAC Insured             
    Nevada – 6.7%             
2,500    Clark County, Nevada, Motor Vehicle Fuel Tax Highway Improvement Revenue Bonds, Series 2003,    7/13 at 100.00    AAA    2,571,350 
     5.000%, 7/01/23 – AMBAC Insured             
    Director of Nevada State Department of Business and Industry, Revenue Bonds, Las Vegas             
    Monorail Project, First Tier, Series 2000:             
2,360     0.000%, 1/01/21 – AMBAC Insured    No Opt. Call    AAA    1,156,353 
3,500     0.000%, 1/01/22 – AMBAC Insured    No Opt. Call    AAA    1,626,205 
6,025     5.375%, 1/01/40 – AMBAC Insured    1/10 at 100.00    AAA    6,192,134 
1,515    Reno, Nevada, Capital Improvement Revenue Bonds, Series 2002, 5.500%, 6/01/21 – FGIC Insured    6/12 at 100.00    AAA    1,614,763 
2,555    Reno, Nevada, Capital Improvement Revenue Bonds, Series 2002, 5.500%, 6/01/21 (Pre-refunded    6/12 at 100.00    AAA    2,756,257 
     6/01/12) – FGIC Insured             
18,455    Total Nevada            15,917,062 
    New Hampshire – 0.2%             
490    New Hampshire Housing Finance Agency, Single Family Mortgage Acquisition Bonds, Series 2001A,    5/11 at 100.00    Aa2    492,347 
     5.600%, 7/01/21 (Alternative Minimum Tax)             
    New Jersey – 2.3%             
2,500    New Jersey Health Care Facilities Financing Authority, Revenue Bonds, Somerset Medical Center,    7/13 at 100.00    Baa3    2,542,075 
     Series 2003, 5.500%, 7/01/23             
    Tobacco Settlement Financing Corporation, New Jersey, Tobacco Settlement Asset-Backed Bonds,             
    Series 2002:             
1,780     5.750%, 6/01/32    6/12 at 100.00    BBB    1,858,249 
1,000     6.000%, 6/01/37    6/12 at 100.00    BBB    1,054,050 
5,280    Total New Jersey            5,454,374 
    New Mexico – 1.7%             
4,000    University of New Mexico, FHA-Insured Mortgage Hospital Revenue Bonds, Series 2004, 4.625%,    7/14 at 100.00    AAA    3,925,600 
     7/01/25 – FSA Insured             
    New York – 1.3%             
1,000    Dormitory Authority of the State of New York, FHA-Insured Mortgage Revenue Bonds, Kaleida    2/14 at 100.00    AAA    1,020,420 
     Health, Series 2004, 5.050%, 2/15/25             
1,600    Dormitory Authority of the State of New York, Revenue Bonds, Mount Sinai NYU Health Obligated    7/10 at 101.00    Ba1    1,712,432 
     Group, Series 2000A, 6.500%, 7/01/17             
145    Long Island Power Authority, New York, Electric System General Revenue Bonds, Series 1998A,    6/08 at 101.00    AAA    149,991 
     5.125%, 12/01/22 (Pre-refunded 6/01/08) – FSA Insured             
305    Long Island Power Authority, New York, Electric System General Revenue Bonds, Series 1998A,    6/08 at 101.00    AAA    313,583 
     5.125%, 12/01/22 – FSA Insured             
3,050    Total New York            3,196,426 
    North Carolina – 1.4%             
500    Appalachian State University, North Carolina, Utilities System Revenue Refunding Bonds, Series    5/08 at 102.00    AAA    511,630 
     1998, 5.000%, 5/15/24 – MBIA Insured             
2,195    North Carolina Eastern Municipal Power Agency, Power System Revenue Refunding Bonds, Series    7/06 at 100.00    BBB    2,207,709 
     1993B, 5.500%, 1/01/21             
500    Raleigh Durham Airport Authority, North Carolina, Airport Revenue Bonds, Series 2001A, 5.250%,    5/11 at 101.00    Aaa    524,650 
     11/01/17 – FGIC Insured             
3,195    Total North Carolina            3,243,989 
    Ohio – 0.5%             
300    Lebanon, Ohio, Electric System Mortgage Revenue Bonds, Series 2001, 5.500%, 12/01/17 –    12/10 at 101.00    AAA    320,106 
     AMBAC Insured             
880    Ohio Housing Finance Agency, GNMA Mortgage-Backed Securities Program Residential Mortgage    9/07 at 102.00    Aaa    904,446 
     Remarketed Revenue Bonds, Series 1997A-1, 6.050%, 9/01/17 (Alternative Minimum Tax)             
1,180    Total Ohio            1,224,552 
    Oklahoma – 2.1%             
1,000    Norman Regional Hospital Authority, Oklahoma, Hospital Revenue Bonds, Series 2005,    9/16 at 100.00    BBB–    1,007,320 
     5.375%, 9/01/36             
4,000    Oklahoma Development Finance Authority, Revenue Bonds, St. John Health System, Series 2004,    2/14 at 100.00    AA    4,059,040 
     5.000%, 2/15/24             
5,000    Total Oklahoma            5,066,360 
    Pennsylvania – 0.8%             
500    Pennsylvania Higher Educational Facilities Authority, Revenue Bonds, Widener University,    7/13 at 100.00    BBB+    512,700 
     Series 2003, 5.250%, 7/15/24             
700    Pennsylvania Turnpike Commission, Turnpike Revenue Bonds, Series 2004A, 5.500%, 12/01/31 –    12/14 at 100.00    AAA    750,351 
     AMBAC Insured             
520    Pennsylvania, General Obligation Bonds, Second Series 2001, 5.000%, 9/15/20 – FSA Insured    9/11 at 101.00    AAA    538,122 
1,720    Total Pennsylvania            1,801,173 
    South Carolina – 7.7%             
1,000    Dorchester County School District 2, South Carolina, Installment Purchase Revenue Bonds,    12/14 at 100.00    A    1,041,860 
     GROWTH, Series 2004, 5.250%, 12/01/20             
10,000    Greenville County School District, South Carolina, Installment Purchase Revenue Bonds, Series    12/12 at 101.00    AA– (3)    11,083,400 
     2002, 5.875%, 12/01/19 (Pre-refunded 12/01/12)             
1,500    Lexington County Health Service District, South Carolina, Hospital Revenue Refunding and    11/13 at 100.00    A    1,616,520 
     Improvement Bonds, Series 2003, 6.000%, 11/01/18             
2,500    South Carolina JOBS Economic Development Authority, Economic Development Revenue Bonds, Bon    11/12 at 100.00    A–    2,600,150 
     Secours Health System Inc., Series 2002A, 5.625%, 11/15/30             
1,720    Tobacco Settlement Revenue Management Authority, South Carolina, Tobacco Settlement    5/11 at 101.00    BBB    1,803,386 
     Asset-Backed Bonds, Series 2001B, 6.000%, 5/15/22             
16,720    Total South Carolina            18,145,316 
    Texas – 9.1%             
5,000    Brazos River Harbor Navigation District, Brazoria County, Texas, Environmental Facilities    5/12 at 101.00    A–    5,426,200 
     Revenue Bonds, Dow Chemical Company Project, Series 2002A-6, 6.250%, 5/15/33 (Mandatory             
     put 5/15/17) (Alternative Minimum Tax)             
1,000    Dallas Area Rapid Transit, Texas, Senior Lien Sales Tax Revenue Bonds, Series 2001, 5.000%,    12/11 at 100.00    AAA    1,010,590 
     12/01/31 – AMBAC Insured             
6,150    Dallas Independent School District, Dallas County, Texas, General Obligation Refunding Bonds,    2/12 at 100.00    AAA    6,457,008 
     Series 2002, 5.250%, 2/15/20             
360    Dallas-Fort Worth International Airport Public Facility Corporation, Texas, Airport Hotel    1/09 at 100.00    AAA    371,812 
     Revenue Bonds, Series 2001, 5.500%, 1/15/20 – FSA Insured             
2,300    Harris County Health Facilities Development Corporation, Texas, Thermal Utility Revenue Bonds,    11/13 at 100.00    AAA    2,327,439 
     TECO Project, Series 2003, 5.000%, 11/15/30 – MBIA Insured             
3,500    Irving Independent School District, Dallas County, Texas, General Obligation Refunding Bonds,    2/12 at 100.00    AAA    3,534,825 
     Series 2002A, 5.000%, 2/15/31             
    San Antonio, Texas, Water System Revenue Refunding Bonds, Series 1992:             
95     6.000%, 5/15/16 (Pre-refunded 5/15/07) – MBIA Insured    5/07 at 100.00    AAA    96,810 
465     6.000%, 5/15/16 (Pre-refunded 5/15/12) – MBIA Insured    5/12 at 100.00    AAA    513,239 
1,750    Texas, General Obligation Bonds, Water Financial Assistance Program, Series 2003A, 5.125%,    8/13 at 100.00    Aa1    1,751,872 
     8/01/42 (Alternative Minimum Tax)             
20,620    Total Texas            21,489,795 
    Utah – 0.3%             
775    Utah State Building Ownership Authority, Lease Revenue Bonds, State Facilities Master Lease    11/11 at 100.00    AA+    811,851 
     Program, Series 2001B, 5.250%, 5/15/24             
    Washington – 9.4%             
250    Energy Northwest, Washington, Electric Revenue Refunding Bonds, Columbia Generating Station –    7/12 at 100.00    AAA    267,428 
     Nuclear Project 2, Series 2002C, 5.500%, 7/01/17 – MBIA Insured             
5,700    Snohomish County Public Utility District 1, Washington, Generation System Revenue Bonds,    No Opt. Call    Aaa    6,179,256 
     Series 1989, 6.750%, 1/01/12 (ETM)             
3,000    Washington State Healthcare Facilities Authority, Revenue Bonds, Catholic Health Initiatives,    12/07 at 101.00    AAA    3,065,820 
     Series 1997A, 5.125%, 12/01/17 – MBIA Insured             
9,750    Washington State Healthcare Facilities Authority, Revenue Bonds, Sisters of Providence Health    10/11 at 100.00    AAA    10,045,328 
     System, Series 2001A, 5.125%, 10/01/17 – MBIA Insured             
2,430    Washington State Tobacco Settlement Authority, Tobacco Settlement Asset-Backed Revenue Bonds,    6/13 at 100.00    BBB    2,643,111 
     Series 2002, 6.500%, 6/01/26             
21,130    Total Washington            22,200,943 
    West Virginia – 0.7%             
1,635    Marshall County, West Virginia, Special Obligation Refunding Bonds, Series 1992, 6.500%,    No Opt. Call    AAA    1,737,335 
     5/15/10 (ETM)             
    Wisconsin – 1.6%             
230    Badger Tobacco Asset Securitization Corporation, Wisconsin, Tobacco Settlement Asset-Backed    6/12 at 100.00    BBB    244,012 
     Bonds, Series 2002, 6.125%, 6/01/27             
1,000    Wisconsin Health and Educational Facilities Authority, Revenue Bonds, Wheaton Franciscan    8/13 at 100.00    A    1,051,550 
     Services Inc., Series 2003A, 5.500%, 8/15/17             
2,500    Wisconsin, General Obligation Refunding Bonds, Series 2003-3, 5.000%, 11/01/26    11/13 at 100.00    AA–    2,557,600 
3,730    Total Wisconsin            3,853,162 
$      236,875    Total Investments (cost $223,893,789) – 99.0%            234,566,268 
    Other Assets Less Liabilities – 1.0%            2,387,238 
    Net Assets – 100%           $   236,953,506 

(1)    Optional Call Provisions: Dates (month and year) and prices of the earliest optional call or 
    redemption. There may be other call provisions at varying prices at later dates. Certain 
    mortgage-backed securities may be subject to periodic principal paydowns. 
(2)    Ratings: Using the higher of Standard & Poor’s or Moody’s rating. Ratings below BBB by Standard 
    & Poor’s Group or Baa by Moody’s Investor Service, Inc. are considered to be below investment grade. 
(3)    Backed by an escrow or trust containing sufficient U.S. Government or U.S. Government agency 
    securities which ensure the timely payment of principal and interest. Such investments are 
    normally considered to be equivalent to AAA rated securities. 
N/R    Not rated. 
(ETM)    Escrowed to maturity. 

Income Tax Information

The following information is presented on an income tax basis. Differences between amounts for financial statement and federal income tax purposes are primarily due to the treatment of paydown gains and losses, timing differences in recognizing taxable market discount and timing differences in recognizing certain gains and losses on investment transactions.

At June 30, 2006, the cost of investments was $223,514,374.

Gross unrealized appreciation and gross unrealized depreciation of investments at June 30, 2006, were as follows:

Gross unrealized:     
  Appreciation    $11,533,482 
  Depreciation    (481,588) 
Net unrealized appreciation (depreciation) of investments    $11,051,894 

Item 2. Controls and Procedures.

  1. The registrant's principal executive and principal financial officers, or persons performing similar functions, have concluded that the registrant's disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the "1940 Act") (17 CFR 270.30a-3(c))) are effective, as of a date within 90 days of the filing date of this report that includes the disclosure required by this paragraph, based on their evaluation of the controls and procedures required by Rule 30a-3(b) under the 1940 Act (17 CFR 270.30a-3(b)) and Rule 13a-15(b) or 15d-15(b) under the Securities Exchange Act of 1934 (17 CFR 240.13a-15(b) or 240.15d-15(b)).
  2. There were no changes in the registrant's internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act (17 CFR 270.30a-3(d)) that occurred during the registrant's last fiscal quarter that have materially affected, or are reasonably likely to materially affect, the registrant's internal control over financial reporting.

Item 3. Exhibits.

File as exhibits as part of this Form a separate certification for each principal executive officer and principal financial officer of the registrant as required by Rule 30a-2(a) under the 1940 Act (17 CFR 270.30a-2(a)), exactly as set forth below: EX-99 CERT Attached hereto.


SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

(Registrant)         Nuveen Select Tax-Free Income Portfolio        

By (Signature and Title)*          /s/ Jessica R. Droeger                     
                                                    Jessica R. Droeger
                                                    Vice President and Secretary

Date         August 28, 2006        

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

By (Signature and Title)*         /s/ Gifford R. Zimmerman                    
                                                   Gifford R. Zimmerman
                                                   Chief Administrative Officer (principal executive officer) 

Date         August 28, 2006        

By (Signature and Title)*         /s/ Stephen D. Foy                              
                                                   Stephen D. Foy
                                                   Vice President and Controller (principal financial officer) 

Date        August 28, 2006        

* Print the name and title of each signing officer under his or her signature.