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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON , D.C. 20549 FORM 20 - F REGISTRATION STATEMENT PURSUANT TO SECTION 12 ( b ) OR ( g ) OF THE SECURITIES EXCHANGE ACT OF ☐ 1934 ☑ OR ANNUAL REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 For the Fiscal Year Ended December 31 , 2020 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 OR SHELL COMPANY REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Commission file number 1-14878 GERDAU S.A. ( Exact name of Registrant as specified in its charter ) N / A ( Translation of Registrant's name into English ) Federative Republic of Brazil ( Jurisdiction of incorporation or organization ) Av . Dra . Ruth Cardoso , 8,501 - 8 ° floor São Paulo , São Paulo - Brazil CEP 05425-070 ( Address of principal executive offices ) ( Zip code ) Securities registered pursuant to Section 12 ( b ) of the Act : Title of each class Preferred Shares , no par value per share , each represented by American Depositary Shares Securities registered pursuant to Section 12 ( g ) of the Act : None Name of each exchange in which registered New York Stock Exchange Securities for which there is a reporting obligation pursuant to Section 15 ( d ) of the Act : None The total number of issued shares of each class of stock of GERDAU S.A. as of December 31 , 2020 was : 573,627,483 Common Shares , no par value per share 1,146,031,245 Preferred Shares , no par value per Indicate by check mark if the registrant is a well - known seasoned issuer , as defined in Rule 405 of the Securities Act . share > Yes □ No If this report is an annual or transition report , indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15 ( d ) of the Securities Exchange Act of 1934 . □ Yes > No