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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 May 31, 2007, 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 May 31, 2007 (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 controls 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 controls over financial
                        reporting, or caused such internal controls 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 controls 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 controls 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 controls 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 controls over financial
                        reporting.

Dated: July 2, 2007                                By: /s/ Walter S. Woltosz
                                                       -----------------------
                                                       Walter S. Woltosz
                                                       Chief Executive Officer