<PAGE>

                                                                    Exhibit 31.2

                                  CERTIFICATION

            PURSUANT TO SECTION 302 OF THE SARBANES OXLEY ACT OF 2002

I, Dennis E. Valentine, certify that:

      1)    I have reviewed this quarterly report on Form 10-Q of JMAR
            Technologies, Inc.;

      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 registrant as of, and for, the periods presented
            in this quarterly report;

      4)    The registrant's other certifying officer 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)) for the
            registrant and we 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 registrant, 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)    evaluated the effectiveness of the registrant'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

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

      5)    The registrant's other certifying officer and I have disclosed,
            based on our most recent evaluation of internal control over
            financial reporting, to the registrant's auditors and the audit
            committee of the registrant's board of directors:

            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
                  registrant'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
                  registrant's internal control over financial reporting.

                                             By: /s/ Dennis E. Valentine
                                                 ------------------------------
                                                 Dennis E. Valentine
                                                 Chief Financial Officer

August 12, 2005