Mail Stop 4561

      April 14, 2006

Mark Fusco
President and Chief Executive Officer
Aspen Technology, Inc.
Ten Canal Park
Cambridge, MA 02141

Re:	Aspen Technology, Inc.
	Form 10-K for Fiscal Year Ended June 30, 2005
	Forms 10-Q for Fiscal Quarter Ended September 30, 2005 and
	December 31, 2005

Dear Mr. Fusco:

	We have reviewed your response to our letter dated February
28,
2006 in connection with our review of the above referenced filings
and have the following comments.  Please note that we have limited
our review to the matters addressed in the comments below.  We may
ask you to provide us with supplemental information so we may
better
understand your disclosure.  Please be as detailed as necessary in
your explanation.  After reviewing this information, we may raise
additional comments.

      Please understand that the purpose of our review process is
to
assist you in your compliance with the applicable disclosure
requirements and to enhance the overall disclosure in your filing.
We look forward to working with you in these respects.  We welcome
any questions you may have about our comments or any other aspect
of
our review.   Feel free to call us at the telephone numbers listed
at
the end of this letter.

Form 10-K For the Fiscal Year Ended February 28, 2005

Management Report on Internal Control Over Financial Reporting,
page
M-1

1. We note your response to our previous comment 1 where you
indicate
that the post closing adjustments that impacted prior quarters was
less than $400,000.  Please provide a breakdown of the individual
adjustments by quarter and tell us how you determined whether such
adjustments were material to the quarters in which they should
have
been recorded.

Form 10-Q For the Quarterly Period Ended September 30, 2005

Note 4. Stock-Based Compensation, page 8

2. Please refer to comment 7 in our letter dated February 28,
2006.
We have reviewed your response and note that the decrease in the
volatility assumption used to value the stock options was a result
of
determining the volatility assumption for the prior year based on
a
historical analysis looking back three to five years.  Note that
paragraph 285 of SFAS 123 states that historical volatility of the
stock over the most recent period that is generally commensurate
with
the expected option life should be considered in estimating
expected
volatility.  Tell us whether you believe three to five years is
commensurate with the expected option life in the prior year.  If
it
is not, quantify the difference in the prior periods had the
estimated volatility been based on a period commensurate with the
expected lives of the options.

3. With regards to the incorrect volatility assumption that was
used
in the pro forma calculations for the Company`s stock purchase
plan
shares, please confirm that you intend to revise your assumptions
in
your next Form 10-Q filing to properly reflect a volatility of 42%
for such plan.

4. Also, tell us what consideration you have given to include a
discussion of stock-based compensation in your Critical Accounting
Policy disclosures, particularly considering the level of
estimates
and assumptions used in determining the Company`s stock-based
compensation expense.


      * * * * *

      As appropriate, please amend your filing and respond to
these
comments within 10 business days or tell us when you will provide
us
with a response.  Please submit all correspondence and
supplemental
materials on EDGAR as required by Rule 101 of Regulation S-T.  You
may wish to provide us with marked copies of any amendment to
expedite our review.  Please furnish a cover letter with any
amendment that keys your responses to our comments and provides
any
requested information.  Detailed cover letters greatly facilitate
our
review.  Please understand that we may have additional comments
after
reviewing any amendment and your responses to our comments.





	 You may contact Patrick Gilmore at (202) 551-3406 or me at
(202) 551-3730 if you have questions regarding comments on the
financial statements and related matters.

							Sincerely,


							Kathleen Collins
							Accounting Branch Chief

Mark Fusco
Aspen Technology, Inc.
April 14, 2006
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