UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G

Under the Securities Exchange Act of 1934

(Amendment No.     )*

(Name of issuer)

(Title of class of securities)

(CUSIP number)

(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)

¨ Rule 13d-1(c)

x 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).

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

SCHEDULE 13G

Imperva, Inc.

3400 Bridge Parkway

Suite 200

Redwood Shores, CA 94065

Greylock XII Limited Partnership (“GXIILP”).

Greylock XII-A Limited Partnership (“GXIIALP”).

Greylock XII GP Limited Liability Company (“GXIIGPLLC”), the General Partner of GXIILP and GXIIALP.

William W. Helman, a Senior Managing Member of GXIIGPLLC.

Aneel Bhusri, a Senior Managing Member of GXIIGPLLC.

The address of each of the reporting persons is:

c/o Greylock Management Corporation

One Brattle Square

#4

Cambridge, MA 02138

GXIILP Delaware limited partnership

GXIIALP Delaware limited partnership

GXIIGPLLC Delaware limited liability company

Mr. Helman U.S. citizen

Mr. Bhusri U.S. citizen

This Schedule 13G report relates to the Common Stock, par value $0.0001 per share (the “Common Stock”), of Imperva, Inc.

45321L100

Not applicable.

SCHEDULE 13G

As of December 31, 2011: (i) GXIILP was the record holder of 1,279,435 shares of Common Stock (the “GXIILP Shares”); and (ii) GXIIALP was the record holder of 142,158 shares of Common Stock (the “GXIIALP Shares”) together with the GXIILP Shares, the “Record Shares”).

GXIIGPLLC, as the general partner of GXIILP and GXIIALP, may be deemed to beneficially own the Record Shares.

Mr. Helman, as a Senior Managing Member of GXIIGPLLC, may be deemed to beneficially own the Record Shares. Mr. Helman may be deemed to beneficially own 7,631 shares of Common Stock held of record by Greylock XII Principals LLC, as nominee on behalf of Mr. Helman.

Mr. Bhursi, as a Senior Managing Member of GXIIGPLLC, may be deemed to benefically own the Record Shares. Mr. Bhusri may be deemed to beneficially own 4,489 shares Common Stock held of record by Greylock XII Principals LLC, as nominee on behalf of Mr. Bhusri.]

The ownership percentages above are based on an aggregate of 22,101,695 shares of common stock outstanding as reported in the issuer’s Amendment No. 6 to Form S-1 Registration Statement filed November 7, 2011.

SCHEDULE 13G

(ii) Shared power to vote or to direct the vote

(iii) Sole power to dispose or to direct the disposition of

(iv) Shared power to dispose or to direct the disposition of

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following ¨.

Not applicable.

Not applicable.

Each of the Reporting Persons expressly disclaims membership in a “Group” as defined in Rule 13d-1(b)(ii)(J).

Not applicable.

Not applicable. This Schedule 13G is not filed pursuant to Rule 13d-1(b) or Rule 13d-1(c).

SCHEDULE 13G

SIGNATURE

After reasonable inquiry and to the best of the knowledge and belief of each of the undersigned, each of the undersigned hereby certifies that the information set forth in this statement is true, complete and correct.

DATED: February 2, 2012.

Exhibit I

JOINT FILING AGREEMENT

Pursuant to Rule 13d-1(k)(1) under the Securities Exchange Act of 1934, as amended, the undersigned hereby agree that only one statement containing the information required by Schedule 13G need be filed with respect to the ownership by each of the undersigned of the shares of Common Stock of Imperva, Inc.

This Agreement may be executed in any number of counterparts, each of which shall be deemed an original.

DATED: February 2, 2012.