UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of September 2018

Commission File Number 001-33098

Mizuho Financial Group, Inc.

(Translation of registrant’s name into English)

5-5, Otemachi 1-chome

Chiyoda-ku, Tokyo 100- 8176

Japan

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F. Form 20-F  ☒    Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ☐

Indicate by check mark whether the registrant by furnishing the information contained in this Form is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934. Yes  ☐    No  ☒

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b):82-                    .

THIS REPORT ON FORM 6-K SHALL BE DEEMED TO BE INCORPORATED BY REFERENCE INTO THE PROSPECTUS FORMING A PART OF MIZUHO FINANCIAL GROUP, INC.’S REGISTRATION STATEMENT ON FORM F-3 (FILE NO. 333-213187) AND TO BE A PART OF SUCH PROSPECTUS FROM THE DATE ON WHICH THIS REPORT IS FURNISHED, TO THE EXTENT NOT SUPERSEDED BY DOCUMENTS OR REPORTS SUBSEQUENTLY FILED OR FURNISHED.

SIGNATURES

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

This document is an English translation of the Japanese original and is intended for reference purposes only. All questions that may arise within or without courts of law in regard to the meaning of the words, provisions, and stipulations of this document shall be decided in accordance with the Japanese text.

September 25, 2018

Notice on Sale of Shares of Shareholders Whose Whereabouts Are Unknown

To shareholders,

Mizuho Financial Group, Inc. (the “Company”) announces that it has decided to sell the shares held by shareholders whose whereabouts are unknown, pursuant to Article 197, Paragraph 1 of the Companies Act, in order to streamline its share affairs. The details are as follows.

The shareholder numbers, full names, addresses, and numbers of held shares of the shareholders whose shares are to be sold, as recorded on the shareholder registry, will be provided by electronic public notice on September 26, 2018, pursuant to Article 198 of the Companies Act. Please refer to the Company’s website: https://www.mizuho-fg.co.jp/investors/kokoku.html

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Shareholders posted on the public notice are requested to send any inquiries on this matter to the administrator of the shareholder registry below.

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