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 October 2019

Commission File Number: 001-35126

21Vianet Group, Inc.

Guanjie Building, Southeast 1st Floor, 10# Jiuxianqiao East Road,

Chaoyang District

Beijing 100016

The People’s Republic of China

(86 10) 8456 2121

(Address, including zip code, and telephone number, including area code, of Registrant’s principal executive offices)

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):  ☐

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.

Date: October 15, 2019

Exhibit Index

Exhibit 99.1 - Press Release

Exhibit 99.1

21Vianet Group, Inc. Announces New Capital Structure Initiative to

Enhance the Stability of Its Corporate Structure

BEIJING, Oct. 14, 2019 (GLOBE NEWSWIRE) — 21Vianet Group, Inc. (Nasdaq: VNET) (“21Vianet” or the “Company”), a leading carrier- and cloud-neutral Internet data center services provider in China, today announced that it has entered into an agreement with Personal Group Limited (the “Purchaser”), a British Virgin Islands company wholly owned by Mr. Sheng Chen, the Executive Chairman of the Board of Directors of the Company, pursuant to which the Company agrees to issue up to 60,000 newly created Class C ordinary shares to the Purchaser, subject to certain existing shareholders’ participation right as discussed below, at a price of US$1.35 per share, which is equal to the volume weighted average price of the Company’s American depositary shares (“ADSs”) for the 30 trading days up to and including October 11, 2019, adjusted by the ADS-to-share ratio. Each ADS represents six Class A ordinary shares of the Company.

Pursuant to an investor right agreement, two of the Company’s existing shareholders, King Venture Holdings Limited and Xiaomi Ventures Limited, have the participation right to subscribe up to 5,049 and 1,468 Class C ordinary shares, respectively, on the same terms as the Purchaser. If these two shareholders exercise their participation right, the number of Class C ordinary shares issued to the Purchaser will be reduced accordingly.

This issuance of the newly created Class C ordinary shares is an initiative by the Company to enhance its ability to execute business strategies over the long term under the leadership of the Company’s board and senior management. Class C ordinary shares entitle the holders thereof the same rights as Class A ordinary shares except for veto right on three corporate matters and conversion right. Please see Annex A hereto for the rights of Class C ordinary shares.

The issuance has been approved by the Company’s audit committee and board of directors.

About 21Vianet

21Vianet Group, Inc. is a leading carrier- and cloud-neutral Internet data center services provider in China. 21Vianet provides hosting and related services, including IDC services, cloud services, and business VPN services to improve the reliability, security and speed of its customers’ Internet infrastructure. Customers may locate their servers and equipment in 21Vianet’s data centers and connect to China’s Internet backbone. 21Vianet operates in more than 30 cities throughout China, servicing a diversified and loyal base of nearly 5,000 hosting and related enterprise customers that span numerous industries ranging from Internet companies to government entities and blue-chip enterprises to small- to mid-sized enterprises.

Safe Harbor Statement

This announcement contains forward-looking statements. These forward-looking statements are made under the “safe harbor” provisions of the U.S. Private Securities Litigation Reform Act of 1995. These statements can be identified by terminology such as “will,” “expects,” “anticipates,” “future,” “intends,” “plans,” “believes,” “estimates” and similar statements. Statements that are not historical facts, including statements about 21Vianet’s beliefs and expectations, are forward-looking statements. Forward-looking statements involve inherent risks and uncertainties. A number of factors could cause actual results to differ materially from those contained in any forward-looking statement. Further information regarding these and other risks is included in 21Vianet’s reports filed with, or furnished to, the Securities and Exchange Commission. All information provided in this press release and in the attachments is as of the date of this press release, and 21Vianet undertakes no duty to update such information, except as required under applicable law.

Investor Relations Contacts:

21Vianet Group, Inc.

Rene Jiang

+86 10 8456 2121

IR@21Vianet.com

Julia Jiang

+86 10 8456 2121

IR@21Vianet.com

ICR, Inc.

Jack Wang

+1 (646) 405-4922

IR@21Vianet.com

Annex A

Rights of Class C Ordinary Shares

for the avoidance of doubt, the creation of any pledge, charge, encumbrance or other third party right of whatever description on any of Class C ordinary shares to secure contractual or legal obligations shall not be deemed as a sale, transfer, assignment or disposition unless and until any such pledge, charge, encumbrance or other third party right is enforced and results in a third party that is not an Affiliate of the holder holding directly or indirectly beneficial ownership or voting power through voting proxy or otherwise to the related Class C ordinary shares, in which case all the related Class C ordinary shares shall be automatically converted into the same number of Class A ordinary shares; or

for the avoidance of doubt, the creation of any pledge, charge, encumbrance or other third party right of whatever description on the issued and outstanding voting securities or the assets of a holder of Class C ordinary shares that is an entity to secure contractual or legal obligations shall not be deemed as a sale, transfer, assignment or disposition under this clause (b) unless and until any such pledge, charge, encumbrance or other third party right is enforced and results in a third party that is not an Affiliate of the holder holding directly or indirectly beneficial ownership or voting power through voting proxy or otherwise to the related issued and outstanding voting securities or the assets.