First Amendment to Credit Agreement, dated as of August 21, 2006, among the Registrant, the various leaders party thereto and Deutsche Bank Trust Company Americas, as Administrative Agent

Exhibit 4.1

CONFORMED COPY

FIRST AMENDMENT TO CREDIT AGREEMENT

     FIRST AMENDMENT TO CREDIT AGREEMENT (this “Amendment”), dated as of August 21, 2006, among AMERISTAR CASINOS, INC., a Nevada corporation (the “Borrower”), the various lenders party to the Credit Agreement referred to below (the “Lenders”) and DEUTSCHE BANK TRUST COMPANY AMERICAS, as Administrative Agent (all capitalized terms used herein and not otherwise defined herein shall have the respective meanings provided such terms in the Credit Agreement as defined below).

W I T N E S S E T H:

     WHEREAS, the Borrower, the Lenders, the Administrative Agent and the other agents party thereto are party to a Credit Agreement, dated as of November 10, 2005 (as amended, modified or supplemented through the date hereof, the “Credit Agreement”);

     WHEREAS, the Borrower has requested that the Lenders agree to certain amendments to the Credit Agreement; and

     WHEREAS, the Borrower and the Lenders wish to amend the Credit Agreement as provided herein;

     NOW, THEREFORE, it is agreed:

     1. Section 9.03 of the Credit Agreement is hereby amended by (x) deleting the text “and” appearing in sub-clause (i) of said Section, (y) deleting the period (“.”) appearing in sub-clause (ii) of said Section and inserting “; and” in lieu thereof and (z) adding the following new sub-clause (iii) to said Section:

“(iii) in addition to any Dividends permitted to be made pursuant to sub-clauses (i) and (ii) above, so long as no Default or Event of Default exists or would result therefrom, the Borrower may make cash repurchases of its capital stock so long as the aggregate amount paid (or value of property distributed) in respect of all such Dividends shall not exceed $125,000,000.”.

     2. The Borrower hereby represents and warrants that (i) no Default or Event of Default exists as of the First Amendment Effective Date (as defined below) both before and after giving effect to this Amendment and (ii) on the First Amendment Effective Date, both before and after giving effect to this Amendment, all representations and warranties (other than those representations made as of a specified date) contained in the Credit Agreement and in the other Credit Documents are true and correct in all material respects.

     3. This Amendment shall become effective on the date (the “First Amendment Effective Date”) when the Required Lenders and the Borrower shall have signed a counterpart hereof (whether the same or different counterparts) and shall have delivered (including by way of facsimile transmission) the same to the Administrative Agent at White & Case LLP, 1155 Avenue of the Americas, New York, NY 10036, Attention: May Yip-Daniels (facsimile number ###-###-####).

     4. This Amendment is limited as specified and shall not constitute a modification, acceptance or waiver of any other provision of the Credit Agreement or any other Credit Document.

     5. This Amendment may be executed in any number of counterparts and by the different parties hereto on separate counterparts, each of which counterparts when executed and delivered shall be an original, but all of which shall together constitute one and the same instrument. A complete set of counterparts shall be lodged with the Borrower and the Administrative Agent.

     6. THIS AMENDMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK.

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     IN WITNESS WHEREOF, the parties hereto have caused their duly authorized officers to execute and deliver this Amendment as of the date first above written.