Although hydrogen peroxide is generated in cells by normal metabolism, the reaction of the stress or by treatment of the cells with 0.4 mmol/L of hydrogen peroxide for 8～24 hours can result in DNA damage. 8-hydroxyguanine is a typical hydroxyl radical-induced products in DNA.The yields of the 8-hydroxyguanine in DNA isolated from H₂O₂-treated HL-60 cells in different ways were reported.The 8-hydroxyguanine in the cells treated in more than 0.4 mmol/L H₂O₂ for eight hours.In order to identify the 8-hydroxyguanine, the result was confirmed by CGC/MS-SIM. The results suggested that the nuclear DNA damage in cells caused by H₂O₂ may be involved in formation of hydroxyl radicals.