Sec Form 4 Filing - O'Brien Kenneth William @ GAIN Capital Holdings, Inc. - 2012-01-03

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person O'Brien Kenneth William 2. Issuer Name and Ticker or Trading Symbol GAIN Capital Holdings, Inc. [ GCAP] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Sr VP, Int'l Operations (Last) (First) (Middle) C/O GAIN CAPITAL HOLDINGS, INC., 135 U.S. HIGHWAY 202/206 3. Date of Earliest Transaction (MM/DD/YY) 01/03/2012 (Street) BEDMINSTER, NJ07921 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price Common Stock ( 1 ) 01/03/2012 M 1,697 A $ 3.83 9,319 ( 3 ) ( 4 ) D Common Stock ( 2 ) 01/03/2012 S 1,697 D $ 6.81 7,622 ( 3 ) ( 4 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Stock Option (Right to Buy) $ 3.83 01/03/2012 M 1,697 ( 5 ) ( 5 ) Common Stock 1,697 $ 0 25,441 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other O'Brien Kenneth William C/O GAIN CAPITAL HOLDINGS, INC. 135 U.S. HIGHWAY 202/206 BEDMINSTER, NJ07921 Sr VP, Int'l Operations Signatures /s/ Kenneth O?Brien 01/05/2012 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Reflects shares acquired upon exercise of stock options listed in Table II below pursuant to a sales plan dated June 3, 2011, which complies with the requirements of Rule 10b5-1(c)(1) under the Securities and Exchange Act of 1934, as amended. ( 2 )The shares were sold pursuant to the June 3, 2011 sales plan. ( 3 )Includes 6000 shares acquired through a restricted stock award on March 23, 2011. Such shares ratably vest 25% per year on each of the first four anniversaries of the grant date. As of the date of this report, 0 shares are vested and 6000 remain unvested. ( 4 )Includes 1,622 shares acquired on July 1, 2011 through an employee stock purchase plan. ( 5 )Such stock options were granted on July 28, 2010 and vest ratably over four years, with one-quarter of the options vesting on each of the first four anniversaries of the grant date. The options have a term of ten years. As of the date of this report, 0 are vested and 25,441 are unvested.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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