Objective To study the effect of vanadium on antioxidase activity in liver microsome and mitochondrion of rats. Methods 40 Wistar rats were randomly divided into 7 groups, 6 experimental groups, 1 control group. The rats in experimental groups were treated with ammonium metavanadate through drinking water at the doses of 1.25, 2.5, 5, 10, 20 and 40 mg/kg respectively for 20 consecutive days. The rats in control group were treated with distilled water. GSH-Px, CAT activity in liver microsome and SOD activity, MDA content in liver mitochondrion were determined. Results GSH-Px, CAT, SOD activity decreased and MDA content increased as ammonium metavanadate dosage increased. Compared with the control group, GSH-Px and CAT activity in 5, 10, 20 and 40 mg/kg groups decreased significantly(P