Exhibit 99.1

Certification Required by Section 906 of the Sarbanes-Oxley Act of 2002.

Written Statement of Chairman and Chief Executive Officer and Principal Financial Officer Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002

I, Alfred P. West, Jr., Chairman and Chief Executive Officer, and Dennis J McGonigle, Chief Financial Officer of SEI Investments Company; a Pennsylvania corporation (the “Company”), hereby certify that, based on our knowledge:

(a)

The Quarterly Report on Form 10-Q of the Company for the three months ended March 31, 2003 filed on the date hereof with the Securities and Exchange Commission (the “Report”) fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934; and

(b)

The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company.