Objective: To study the effects of gatifloxacin on hepatic microsome cytochrornes P450.Methods: The male Wistar rats were divided into four groups, they were control group and gatifloxacin groups, the control rats were received saline only, the rats of gatifloxacin groups were administered at a dose of 80 mg?kg-1(low dose group,LG), 160 mg?kg-1(medial dose group, MG) and 240 mg?kg-1(high dose group, HG) respectively by peritoneal injection(i.p), qd for consecutive seven days.Liver microsome v was prepared by different velocity centrifugation.