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Exhibit 10.63

[AspenTechnology Letterhead/Logo]

August 18, 2003

Charles Kane
Senior Vice President and CFO

Dear Chuck:

This letter amendment references the offer letter between you and AspenTech
dated June 16, 2003 (the "Agreement") regarding your employment with AspenTech.
Under the terms of the Agreement, AspenTech agreed that, following stockholder
approval of the Advent transaction, it would grant you an option to purchase a
number of shares of AspenTech common stock which would maintain your
pre-transaction equity participation percentage in AspenTech (the "Option"). As
you know, the Advent transaction was approved by AspenTech stockholders and
closed on August 14, 2003.

AspenTech acknowledges that you have voluntarily agreed to reduce the number of
shares subject to the Option to which you were entitled in order to make more
options available for the general employee option pool. You hereby confirm, by
execution of this letter amendment, that the option granted to you on August 18,
2003 for 189,216 shares of AspenTech common stock constitutes full satisfaction
of AspenTech's obligations under the Agreement to grant the Option and that the
terms of the Agreement do not entitle you to any additional stock option grants.
All other terms of the Agreement, including those contingent upon the closing of
the Advent transaction, remain in full force and effect.

Best regards,        
/s/  HELEN MOYE      
 
/s/  CHARLES KANE      
 
Sept. 26, 2003

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Helen Moye   Charles Kane   Date Sr. VP Human Resources
Aspen Technology, Inc.   Senior Vice President and CFO    

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Exhibit 10.63