Exhibit 99.1 Certification of the Chief Executive Officer Pursuant to Section 906 of the Sarbanes-Oxley Act of 2002 In connection with this amendment no.1 to annual report on Form 10-K/A (the "Report") of Nanophase Technologies Corporation (the "Company"), I, Joseph Cross, Chief Executive Officer of the Company, certify, pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, that: 1. The Report fully complies with the requirements of section 13(a) or 15(d) of the Securities Exchange Act of 1934; and 2. The information contained in the Report fairly presents, in all material respects, the financial condition and result of operations of the Company. Date: May 23, 2003 /s/ JOSEPH E. CROSS --------------------------------------- Joseph E. Cross Chief Executive Officer