UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

(Rule 13d-102)

Information to be Included in Statements Filed Pursuant to § 240.13d-1(b), (c)

and (d) and Amendments Thereto Filed Pursuant to § 240.13d-2.

Under the Securities Exchange Act of 1934

(Amendment No.     )*

Cheetah Mobile Inc.

(Name of Issuer)

Class A Ordinary Shares, par value US$0.000025 per share,

including Class A Ordinary Shares represented by

American Depositary Shares (each representing ten Class A Ordinary Shares)

(Title of Class of Securities)

American Depositary Shares: 163075104

(CUSIP Number)

May 7, 2014

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

¨ Rule 13d-1(b)

x Rule 13d-1(c)

¨ Rule 13d-1(d)

The information required in the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

Cheetah Mobile Inc.

12/F, Fosun International Center Tower

No. 237 Chaoyang North Road

Chaoyang District, Beijing 100022

People’s Republic of China

#06-18, The Atrium@Orchard,

Singapore 238891

#06-18, The Atrium@Orchard,

Singapore 238891

#06-18, The Atrium@Orchard,

Singapore 238891

Les Cascades,

Edith Cavell Street,

Port Louis, Mauritius

Les Cascades,

Edith Cavell Street,

Port Louis, Mauritius

Class A Ordinary Shares, par value US$0.000025 per share.

American Depositary Shares: 163075104

Not applicable.

Upon completion of the issuer’s initial public offering scheduled on May 13, 2014, Baytree directly owned 1,000,000 American Depositary Shares, representing a total of 10,000,000 Class A Ordinary Shares. Baytree is wholly-owned by Dunearn, which in turn is wholly-owned by Seletar, which in turn is wholly-owned by Temasek Capital, which in turn is wholly-owned by Temasek Holdings.

Accordingly, upon completion of the issuer’s initial public offering scheduled on May 13, 2014, each of Temasek Holdings, Temasek Capital, Seletar and Dunearn may be deemed to have beneficially owned the 10,000,000 Class A Ordinary Shares owned by Baytree. There are no changes to the above shareholdings as of the date of this Schedule.

Upon completion of the issuer’s initial public offering scheduled on May 13, 2014, the Class A Ordinary Shares that may be deemed to have been beneficially owned by Temasek Holdings, Temasek Capital, Seletar and Dunearn, and beneficially owned by Baytree, constituted approximately 6.42% of the Class A Ordinary Shares outstanding.

All percentage calculations in this Schedule are based on 155,714,285 Class A Ordinary Shares reported by Cheetah Mobile Inc. as outstanding immediately upon completion of its initial public offering in its prospectus dated May 7, 2014 and filed with the SEC on May 8, 2014.

With respect to the shared power to vote, or to direct the vote, and to dispose, or to direct the disposition of, the Shares, please see Item 4(a) above regarding qualifications as to beneficial ownership.

0.

Temasek Holdings: 10,000,000

Temasek Capital: 10,000,000

Seletar: 10,000,000

Dunearn: 10,000,000

Baytree: 10,000,000

0.

Temasek Holdings: 10,000,000

Temasek Capital: 10,000,000

Seletar: 10,000,000

Dunearn: 10,000,000

Baytree: 10,000,000

Not Applicable.

Not Applicable.

Not Applicable.

Not Applicable.

Not Applicable

By signing below, I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under §240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Exhibit Index

Exhibit A

JOINT FILING AGREEMENT

We, the signatories of this Statement on Schedule 13G to which this Agreement is attached, hereby agree that such Statement is, and any amendments thereto filed by any of us will be, filed on behalf of each of us.