GGB Gerdau SA

FORM 6-K

U.S. SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

REPORT OF FOREIGN PRIVATE ISSUER

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

SECURITIES EXCHANGE ACT OF 1934

Dated February 25, 2016

Commission File Number 1-14878

GERDAU S.A.

(Exact Name as Specified in its Charter)

N/A

(Translation of Registrant’s Name)

Av. Farrapos 1811

Porto Alegre, Rio Grande do Sul - Brazil CEP 90220-005

(Address of principal executive offices)

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

Form 20-F  x             Form 40-F  o

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): o

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): o

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes  o       No  x

If “Yes” is marked, indicate below the file number assigned to the registrant in connection with Rule 12g3-2(b):  Not applicable.

SIGNATURES

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

Date:  February 25, 2016

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EXHIBIT INDEX

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Exhibit 99.1

NOTICE TO THE MARKET

Gerdau hereby announces that the Brazilian Federal Police is in its offices this morning in connection with Operation Zelotes. It clarifies that it has no further information at the moment, but is fully cooperating with the Federal Police investigations.

It also emphasizes that, based on its ethical principles, Gerdau did not provide any authorization for its name to be used in alleged unlawful negotiations, and strongly repudiates any action taken for this purpose.

Gerdau reiterates that it has set strict ethical standards for its dealings with public agencies and reaffirms that it is, as it has always been, at the disposal of competent authorities to provide any clarifications that may be requested.

Porto Alegre, February 25, 2016.

Harley Lorentz Scardoelli

Executive Vice President

Investor Relations Director