Schedule 13D/Amendment No. 4

Date: December 30, 2011

SAIF Partners IV L.P.

/s/ Andrew Y. Yan

Andrew Y. Yan

Director of SAIF IV GP Capital Ltd., which is the General Partner of SAIF IV GP, L.P., which is the General Partner of SAIF Partners IV L.P.

SC 13D/A 1 d276013dsc13da.htm SCHEDULE 13D/AMENDMENT NO. 4 Schedule 13D/Amendment No. 4

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 4)*

SINOVAC BIOTECH LTD.

(Name of issuer)

Common Shares

(Title of class of securities)

P8696W104

(CUSIP number)

Andrew Y. Yan

c/o SAIF Advisors Limited,

Suite 2516-2520, Two Pacific Place

88 Queensway

Hong Kong

+852 2918-2200

(Name, address and telephone number of person authorized to receive notices and communications)

December 29, 2011

(Date of event which requires filing of this statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box. x

Note: Schedules filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See Rule 13d-7 for other parties to whom copies are to be sent.

The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

The information required on 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 13D


CUSIP No. P8696W104		Page 2 of 6 Pages


(1)	Names of reporting persons SAIF Partners IV L.P.
(2)	Check the appropriate box if a member of a group (see instructions) (a) ¨ (b) x
(3)	SEC use only
(4)	Source of funds (see instructions) WC
(5)	Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e) ¨
(6)	Citizenship or place of organization Cayman Islands
Number of shares beneficially owned by each reporting person with:		(7)	Sole voting power 10,595,720 Common Shares
		(8)	Shared voting power 0
		(9)	Sole dispositive power 10,595,720 Common Shares
		(10)	Shared dispositive power 0
(11)	Aggregate amount beneficially owned by each reporting person 10,595,720 Common Shares
(12)	Check if the aggregate amount in Row (11) excludes certain shares (see instructions) ¨
(13)	Percent of class represented by amount in Row (11) 19.4%¹
(14)	Type of reporting person (see instructions) PN

¹	Based upon 54,641,304 Common Shares outstanding as of September 30, 2011, as reported by the Issuer in a Form 6-K filed on December 8, 2011.

SCHEDULE 13D


CUSIP No. P8696W104		Page 3 of 6 Pages


(1)	Names of reporting persons SAIF IV GP, L.P.
(2)	Check the appropriate box if a member of a group (see instructions) (a) ¨ (b) x
(3)	SEC use only
(4)	Source of funds (see instructions) WC
(5)	Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e) ¨
(6)	Citizenship or place of organization Cayman Islands
Number of shares beneficially owned by each reporting person with:		(7)	Sole voting power 10,595,720 Common Shares
		(8)	Shared voting power 0
		(9)	Sole dispositive power 10,595,720 Common Shares
		(10)	Shared dispositive power 0
(11)	Aggregate amount beneficially owned by each reporting person 10,595,720 Common Shares
(12)	Check if the aggregate amount in Row (11) excludes certain shares (see instructions) ¨
(13)	Percent of class represented by amount in Row (11) 19.4%²
(14)	Type of reporting person (see instructions) PN

²	Based upon 54,641,304 Common Shares outstanding as of September 30, 2011, as reported by the Issuer in a Form 6-K filed on December 8, 2011.

SCHEDULE 13D


CUSIP No. P8696W104		Page 4 of 6 Pages


(1)	Names of reporting persons SAIF IV GP Capital Ltd.
(2)	Check the appropriate box if a member of a group (see instructions) (a) ¨ (b) x
(3)	SEC use only
(4)	Source of funds (see instructions) WC
(5)	Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e) ¨
(6)	Citizenship or place of organization Cayman Islands
Number of shares beneficially owned by each reporting person with:		(7)	Sole voting power 10,595,720 Common Shares
		(8)	Shared voting power 0
		(9)	Sole dispositive power 10,595,720 Common Shares
		(10)	Shared dispositive power 0
(11)	Aggregate amount beneficially owned by each reporting person 10,595,720 Common Shares
(12)	Check if the aggregate amount in Row (11) excludes certain shares (see instructions) ¨
(13)	Percent of class represented by amount in Row (11) 19.4%³
(14)	Type of reporting person (see instructions) CO

³	Based upon 54,641,304 Common Shares outstanding as of September 30, 2011, as reported by the Issuer in a Form 6-K filed on December 8, 2011.

This Amendment No. 4 to Schedule 13D is being filed on behalf of each of SAIF Partners IV L.P., SAIF IV GP, L.P., and SAIF IV GP Capital Ltd. (collectively, the “SAIF Entities”), to amend the Schedule 13D filed on behalf of the SAIF entities on May 31, 2011, as amended by Amendment No.1 to Schedule 13D filed on August 23, 2011, Amendment No.2 to Schedule 13D filed on September 30, 2011 and Amendment No.3 to Schedule 13D filed on November 29, 2011. The information in each Item below amends the information disclosed under the corresponding Item of Schedule 13D. Capitalized terms defined in the Schedule 13D are used herein with their defined meaning. The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is relevant.

Item 5. Interest in Securities of the Issuer

(a) Each of the SAIF Entities may be deemed to have beneficial ownership of an aggregate of 10,595,720 Common Shares. Such Common Shares represented approximately 19.4% of the outstanding Common Shares that were deemed to be outstanding for purposes of calculating the beneficial ownership of the SAIF Entities under Section 13(d) of the Act. All percentages of Common Shares beneficially owned described in this statement are based upon 54,641,304 Common Shares outstanding as of September 30, 2011, as reported by the Issuer in a Form 6-K filed on December 8, 2011.

(b) Each of the SAIF Entities may be deemed to exercise sole power to vote or to direct the vote and sole power to dispose or to direct the disposition of an aggregate of 10,595,720 Common Shares.

		September 30,		September 30,
Date	Number of Common Shares Purchased		Purchase Price per Common Share (US$)
12/16/2011		61,700		2.2000
12/19/2011		249,684		2.1899
12/20/2011		23,200		2.1950
12/29/2011		370,000		2.2800

To the knowledge of the SAIF Entities, Mr. Yan has not effected any transactions in the Common Shares since the filing of Amendment No.3 to Schedule 13D.

(d) To the knowledge of the SAIF Entities, no other person has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, Common Shares.

(e) Not applicable.

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.