**EXHIBIT 31.2**

**CERTIFICATION OF PERIODIC REPORT UNDER SECTION 302 OF**

**THE SARBANES-OXLEY ACT OF 2002**

I, Andrew Hamer, certify that: 

1. I have reviewed thisquarterly report on Form 10-Q of Keynote Systems, Inc.; 

2. Based on my knowledge, this quarterly report does not contain any untrue statement of amaterial 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 thefinancial condition, results of operations and cash flows of the registrant as of, and for, the periods presented in this quarterly report; 

4. Theregistrant’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)) and internal control over financial reporting (as definedin Exchange Act Rules 13a-15(f) and 15d-15(f)) for the registrant and have: 

a) Designed such disclosure controls and procedures, or caused such disclosurecontrols 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 theperiod in which this quarterly report is being prepared; 

b) Designed such internal control over financial reporting, or caused such internal control overfinancial 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 acceptedaccounting principles; 

c) Evaluated the effectiveness of the registrant’s disclosure controls and procedures and presented in this report ourconclusions 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 

d) Disclosed in this report any change in the registrant’s internal control over financial reporting that occurred during the registrant’s most recent fiscal quarter that has materially affected, or is reasonably likely tomaterially affect, the registrant’s internal control over financial reporting; and 

5. The registrant’s other certifying officer and I havedisclosed, 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 adverselyaffect the registrant’s ability to record, process, summarize and report financial information; and 

b) Any fraud, whether or not material, thatinvolves management or other employees who have a significant role in the registrant’s internal control over financial reporting. 

Date: May 10,2006