Commission File No. 1-31926

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 12b-25

NOTIFICATION OF LATE FILING

(Check one):  ¨ Form 10-K   ¨ Form 20-F   ¨ Form 11-K   þ Form 10-Q    ¨ Form 10-D   ¨ Form N-SAR ¨ Form N-CSR

For Period Ended: March 31, 2006
o Transition Report on Form 10-K
o Transition Report on Form 20-F
o Transition Report on Form 11-K
o Transition Report on Form 10-Q
o Transition Report on Form N-SAR
For the Transition Period Ended: _____________________

If the notification relates to a portion of the filing checked above, identify the Item(s) to which the notification relates:

PART I — REGISTRANT INFORMATION

Mittal Steel USA Inc.

Full Name of Registrant

Mittal Steel USA ISG Inc.

Former Name if Applicable

1 South Dearborn

Address of Principal Executive Office (Street and Number)

Chicago, Illinois  60603

City, State and Zip Code

PART II — RULES 12b-25(b) AND (c)

If the subject report could not be filed without unreasonable effort or expense and the registrant seeks relief pursuant to Rule 12b-25(b), the following should be completed. (Check box if appropriate)

				(a)		The reason described in reasonable detail in Part III of this form could not be eliminated without unreasonable effort or expense
þ				(b)		The subject annual report, semi-annual report, transition report on Form 10-K, Form 20-F, Form 11-K, Form N-SAR or Form N-CSR, or portion thereof, will be filed on or before the fifteenth calendar day following the prescribed due date; or the subject quarterly report or transition report on Form 10-Q or subject distribution report on Form 10-D, or portion thereof, will be filed on or before the fifth calendar day following the prescribed due date; and
				(c)		The accountant’s statement or other exhibit required by Rule 12b-25(c) has been attached if applicable.

PART III — NARRATIVE

State below in reasonable detail why Forms 10-K, 20-F, 11-K, 10-Q, 10-D, N-SAR, N-CSR, or the transition report or portion thereof, could not be filed within the prescribed time period.

(Attach extra Sheets if Needed)

The Quarterly Report on Form 10-Q for the quarter ended March 31, 2006 (the “Form 10-Q”) for Mittal Steel USA Inc. (the “Company”) cannot be completed within the prescribed time period due to a delay in completing the purchase accounting associated with the second-quarter 2005 merger of the predecessor Company with a wholly owned subsidiary of Mittal Steel Company NV (the “Merger”). Furthermore, the Company has needed additional time to review the appraisal report regarding the value of certain assets and to determine if any additional adjustments, resulting from the appraisal report, will be required to finalize purchase accounting adjustments related to the Merger. The delay in completing the Company’s Form 10-Q could not be eliminated without unreasonable effort or expense. The Form 10-Q will be filed as soon as practicable and, in any event, no later than the fifth calendar date following the prescribed due date.

PART IV — OTHER INFORMATION

(1)

Name and telephone number of person to contact in regard to this notification

Carlos M. Hernandez		312		899-3400
(Name)		(Area Code)		(Telephone Number)

(2)

Have all other periodic reports required under Section 13 or 15(d) of the Securities Exchange Act of 1934 or Section 30 of the Investment Company Act of 1940 during the preceding 12 months or for such shorter period that the registrant was required to file such report(s) been filed ? If answer is no, identify report(s). þ Yes ¨ No

(3)

Is it anticipated that any significant change in results of operations from the corresponding period for the last fiscal year will be reflected by the earnings statements to be included in the subject report or portion thereof? ¨ Yes þ No

If so, attach an explanation of the anticipated change, both narratively and quantitatively, and, if appropriate, state the reasons why a reasonable estimate of the results cannot be made.

                        Mittal Steel USA Inc.                        
(Name of Registrant as Specified in Charter)

has caused this notification to be signed on its behalf by the undersigned hereunto duly authorized.

		Date: May 15, 2006		By:		/s/ Vaidya Sethuraman
						Name: Vaidya Sethuraman Title: Vice President Finance and           Chief Accounting Officer

INSTRUCTION: The form may be signed by an executive officer of the registrant or by any other duly authorized representative. The name and title of the person signing the form shall be typed or printed beneath the signature. If the statement is signed on behalf of the registrant by an authorized representative (other than an executive officer), evidence of the representative’s authority to sign on behalf of the registrant shall be filed with the form.

GENERAL INSTRUCTIONS

1.

This form is required by Rule 12b-25 (17 CFR 240.12b-25) of the General Rules and Regulations under the Securities Exchange Act of 1934.

2.

One signed original and four conformed copies of this form and amendments thereto must be completed and filed with the Securities and Exchange Commission, Washington, D.C. 20549, in accordance with Rule 0-3 of the General Rules and Regulations under the Act. The information contained in or filed with the form will be made a matter of public record in the Commission files.

3.

A manually signed copy of the form and amendments thereto shall be filed with each national securities exchange on which any class of securities of the registrant is registered.

4.

Amendments to the notifications must also be filed on Form 12b-25 but need not restate information that has been correctly furnished. The form shall be clearly identified as an amended notification.

5.

Electronic Filers: This form shall not be used by electronic filers unable to timely file a report solely due to electronic difficulties. Filers unable to submit reports within the time period prescribed due to difficulties in electronic filing should comply with either Rule 201 or Rule 202 of Regulation S-T (§232.201 or §232.202 of this chapter) or apply for an adjustment in filing date pursuant to Rule 13(b) of Regulation S-T (§232.13(b) of this chapter).