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Table of Contents ( Mark One ) > ☐ 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 ㅁ SHELL COMPANY REPORT PURSUANT TO SECTION 13 OR 15 ( d ) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of event requiring this shell company report . For the transition period from Commission file number 001-35126 to 21 Vianet Group , Inc. ( Exact name of Registrant as specified in its charter ) N / A ( Translation of Registrant's name into English ) Cayman Islands ( Jurisdiction of incorporation or organization ) Guanjie Building Southeast 1st Floor , 10 # Jiuxianqiao East Road Chaoyang District Beijing , 100016 The People's Republic of China ( Address of principal executive offices ) Ms. Sharon Xiao Liu , Chief Financial Officer 21 Vianet Group , Inc. Guanjie Building , Southeast 1st Floor 10 # Jiuxianqiao East Road Chaoyang District Beijing , 100016 The People's Republic of China Phone : ( 86 ) 10 8456-2121 Facsimile : ( 86 ) 10 8456-4234 ( Name , Telephone , E - mail and / or Facsimile number and Address of Company Contact Person ) Securities registered or to be registered pursuant to Section 12 ( b ) of the Act :