<PAGE>

                                                                    Exhibit 31.1

                    CERTIFICATION OF CHIEF EXECUTIVE OFFICER
            PURSUANT TO SECTION 302 OF THE SARBANES-OXLEY ACT OF 2002

I, Robert C. Brehm, certify that:

            1. I have reviewed this quarterly report on Form 10-QSB of U.S.
Microbics, Inc.;

            2. Based on my knowledge, this 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 report;

            3. Based on my knowledge, the financial statements, and other
financial information included in this report, fairly present in all material
respects the financial condition, results of operations and cash flows of the
small business issuer as of, and for, the periods presented in this report;

            4. The small business issuer 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 small
business issuer 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 small business issuer,
                       including its consolidated subsidiaries, is made known to
                       us by others within those entities, particularly during
                       the period in which this report is being prepared;

                       b) evaluated the effectiveness of the small business
                       issuer's disclosure controls and procedures and presented
                       in this report our conclusions about the effectiveness of
                       the disclosure controls and procedures, as of the end of
                       the period covered by this report based on such
                       evaluation; and

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

            5. The small business issuer's other certifying officer and I have
disclosed, based on our most recent evaluation of internal control over
financial reporting, to the small business issuer's auditors and the audit
committee of the small business issuer'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 small business issuer'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 small business issuer's internal control over
                      financial reporting.

Date: May 24, 2004

                                                 /s/ Robert C. Brehm
                                                 -------------------
                                                     Robert C. Brehm
                                                     Chief Executive Officer