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                                                                    EXHIBIT 31.1


                          RULE 13A-14(A) CERTIFICATION

                             SIMULATIONS PLUS, INC.
                            a California corporation

                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER

         I, Walter S. Woltosz, Chief Executive Officer of Simulations Plus,
Inc., a California corporation (the "Company"), do hereby certify, in accordance
with Rules 13a-14 and 15d-14, as created pursuant to Section 302(a) of the
Sarbanes-Oxley Act of 2002, with respect to the Quarterly Report on Form 10-QSB
of the Company for the fiscal quarter ended February 28, 2005, as filed with the
Securities and Exchange Commission herewith under Section 15(d) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), that:

     (1)  I have reviewed this Quarterly Report on Form 10-QSB of the Company
          for the fiscal quarter ended February 28, 2005 (the "Quarterly
          Report");

     (2)  Based on my knowledge, this Quarterly Report does not contain any
          untrue statement of a material fact or omit to state a material fact
          necessary to make the statements made, in light of the circumstances
          under which such statements were made, not misleading with respect to
          the period covered by this Quarterly Report;

     (3)  Based on my knowledge, the financial statements, and other financial
          information included in this Quarterly Report, fairly present in all
          material respects the financial condition, results of operations and
          cash flows of the Company as of, and for, the periods presented in
          this Quarterly Report;

     (4)  The Company's other certifying officers and I are responsible for
          establishing and maintaining disclosure controls and procedures (as
          defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) and internal
          control over financial reporting (as defined in Exchange Act Rules
          13a-15(f) and 15(d)-15(f)) for the Company and have:

          (a)  designed such disclosure controls and procedures, or caused such
               disclosure controls and procedures to be designed under our
               supervision, to ensure that material information relating to the
               Company, including its consolidated subsidiaries, is made known
               to us by others within those entities, particularly during the
               period in which this Quarterly Report is being prepared;

          (b)  designed such internal control over financial reporting, or
               caused such internal control over financial reporting to be
               designed under our supervision, to provide reasonable assurance
               regarding the reliability of financial reporting and the
               preparation of financial statements for external purposes in
               accordance with generally accepted accounting principles;

          (c)  evaluated the effectiveness of the Company's disclosure controls
               and procedures and presented in this Quarterly Report our
               conclusions about the effectiveness of the disclosure controls
               and procedures, as of the end of the period covered by this
               Quarterly Report based on such evaluation; and

          (d)  disclosed in this Quarterly Report any change in the Company's
               internal control over financial reporting that occurred during
               the Company's most recent fiscal quarter (the Company's fourth
               fiscal quarter in the case of an annual report) that has
               materially affected, or is reasonable likely to materially
               affect, the Company's internal control over financial reporting;
               and

     (5)  The Company's other certifying officers and I have disclosed, based on
          our most recent evaluation, to the Company's auditors and the audit
          committee of the Company's board of directors (or persons performing
          the equivalent functions):

          (a)  all significant deficiencies and material weaknesses in the
               design or operation of internal control over financial reporting
               which are reasonably likely to adversely affect the Company's
               ability to record, process, summarize and report financial
               information; and

          (b)  any fraud, whether or not material, that involves management or
               other employees who have a significant role in the Company's
               internal control over financial reporting.

Dated: April 14, 2005                          By: /s/ Walter S. Woltosz
                                                   -----------------------------
                                                   Walter S. Woltosz
                                                   Chief Executive Officer