[PROSPECTUS (Subject to Completion) Issued April 20, 2011 12,500,000 American Depositary Shares 21Vianet Group, Inc. Representing 75,000,000 Class A Ordinary Shares 21Vianet Group, Inc. is offering 12,500,000 American depositary shares, or ADSs, each representing six Class A ordinary shares, par value US$0.00001 per share. This is our initial public offering and no public market currently exists for our ADSs or] [75,000,000 Class A Ordinary Shares 21Vianet Group, Inc. CLASS A ORDINARY SHARES, PAR VALUE US$0.00001 PER SHARE in the form of American Depositary Shares UNDERWRITING AGREEMENT April [ — ], 2011 — [ Morgan Stanley & Co. International plc 25 Cabot Square, Canary Wharf London E14 4QA United Kingdom Barclays Capital Inc. 745 Seventh Avenue New York, NY 10019 J.P.] [Our ref VZL\653749\4416045v1 Direct tel +852 2971 3095 Email valerie.law@maplesandcalder.com 21Vianet Group, Inc. M5, 1 Jiuxianqiao East Road Chaoyang District Beijing 100016 People’s Republic of China 20 April 2011 Dear Sirs 21Vianet Group, Inc. Company Registration Statement ADSs Shares We have acted as Cayman Islands legal advisers to 21Vianet Group Inc. (the “ 1 Documents Reviewed For the purposes of] [21Vianet Group, Inc. Share Subscription Agreement December 31, 2010 1 Sunrise Corporate Holding Ltd. Subscriber 2,482,609 Shares Company Articles 2 The Shares will be allotted and issued as fully paid at issue price of US$0.0001 per share. The Subscriber hereby agrees to pay to the Company US$0.0001 per share for the Shares, such amount to be paid to the Company’s] [Consents of Independent Registered Public Accounting Firm We consent to the reference to our firm under the caption “Experts” and to the use of our report dated March 1, 2011 (except for Note 26(d) as to which the date is April 4, 2011), with respect to the consolidated financial statements of 21Vianet Group, Inc., included in Amendment No.3 to the]