Letter Amendment to Employment Offer Letter between Aspen Technology, Inc. and Charles Kane (Stock Option Adjustment)

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.

QuickLinks

Exhibit 10.63