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 December 2011

Commission File Number: 001-35126

21Vianet Group, Inc.

M5, 1 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  x            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.

21Vianet Group, Inc.
By:	/s/ Shang-Wen Hsiao
Name:	Shang-Wen Hsiao
Title:	President and Chief Financial Officer

Date: December 16, 2011

Exhibit Index

Exhibit 99.1 — Press Release Regarding Completion of Acquisition of Managed Network Entities

Exhibit 99.1

21Vianet Group, Inc. Completes

Acquisition of Managed Network Entities

BEIJING, December 15, 2011 — 21Vianet Group, Inc. (NASDAQ: VNET) (“21Vianet” or the “Company”), the largest carrier-neutral Internet data center services provider in China, today announced that it has exercised its option to acquire the remaining 49% equity interest in two companies that provide managed network services, Zhiboxintong (Beijing) Network Technology Co., Ltd. and Beijing Chengyishidai Network Technology Co., Ltd. (together, the “Managed Network Entities”). In September 2010, the Company acquired 51% equity interest in the Management Network Entities with an option to acquire the remaining 49% equity interest before December 31, 2011.

Mr. Josh Chen, Founder, Chairman and Chief Executive Officer of the Company, stated, “We remain committed to further expanding our managed network services to meet our growing customer demand. We are confident that the completion of this acquisition will enable us to further integrate Managed Network Entities’ extensive network and business operations, further streamlining expenses and solidifying our industry leadership.”

Mr. Shang Hsiao, President and Chief Financial Officer of the Company, commented, “Going forward, we continue to believe that the full acquisition of Managed Network Entities will further enhance the revenue growth and profitability of our business in the coming years due to increasing demand for managed network services. In addition, this acquisition is not expected to have any material impact on our previously announced guidance for the fourth quarter of 2011. In the long term, we expect this transaction to have a positive impact on our financial performance.”

About 21Vianet

21Vianet Group, Inc. is the largest carrier-neutral Internet data center services provider in China. 21Vianet provides hosting and related services, managed network services and cloud computing infrastructure services, improving the reliability, security and speed of its customers’ Internet connections through 21Vianet’s Internet infrastructure. Customers may locate their servers and networking equipment in 21Vianet’s data centers and connect to China’s Internet backbone through 21Vianet’s extensive fiber optic network. In addition, 21Vianet’s proprietary smart routing technology, BroadEx, enables customers’ data to be delivered across the Internet in a faster and more reliable manner. 21Vianet operates in 33 cities throughout China, servicing a diversified and loyal base of more than 1,400 customers that span many 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. Among other things, the outlook for the fourth quarter of 2011 and quotations from management in this announcement, as well as 21Vianet’s strategic and operational plans, contain forward-looking statements. 21Vianet may also make written or oral forward-looking statements in its reports filed with, or furnished to, the U.S. Securities and Exchange Commission, in its annual reports to shareholders, in press releases and other written materials and in oral statements made by its officers, directors or employees to third parties. 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, including but not limited to the following: 21Vianet’s goals and strategies; 21Vianet’s expansion plans; the expected growth of the data center services market; expectations regarding demand for, and market acceptance of, 21Vianet’s services; 21Vianet’s expectations regarding keeping and strengthening its relationships with customers; 21Vianet’s plans to invest in research and development to enhance its solution and service offerings; and general economic and business conditions in the regions where 21Vianet provides solutions and services. Further information regarding these and other risks is included in 21Vianet’s reports filed with, or furnished to the Securities and Exchange Commission. 21Vianet does not undertake any obligation to update any forward-looking statement, except as required under applicable law. 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 Contact:

ICR, Inc.

Jeremy Peruski

+1 (646) 405-4922

IR@21Vianet.com

Source: 21Vianet