The purpose of this study was to investigate peroxidative damage and antioxidative defense systems such as superoxide dismutase(SOD), glutathione peroxidase(GSH Px), glutathione S transferase (GST) and vitamin E of liver in rat exposed microwave. Sprague Dawley male rats 200$pm$10gm were randomly assigned to normal and microwave(MW) groups. After rats were irradiated with microwave at frequency of 2.45GHz for 15min, the change patterns of antioxidative defense system and peroxidative damage of liver tissue in MW group were investigated for 16 days(the 2nd, 4th, 6th, 8th and 16th days) compared with those of normal group. The activity of superoxide dismutase(SOD) in MW group was increased at the 2nd day compared with that of normal group, but not significantly. The glutathione peroxidase(GSH Px) in MW group was decreased to 24% and 25% at the 4th and 6th days, respectively, compoared with that of normal group, but GSH Px was increased to level of normal group at the 16th day. The activity of glutathione S transferase(GST) in MW group was decreased at the 2nd day after irradiated with microwave, but GST showed to that of normal group at the 16th day. The content of vitamin E in MW group was lower than that of normal group at the 6th and 8th days after the irradiation, but was recovered to the level of normal group at the 16th days. The content of thi obarbituric acid reactive substances(TBARS) of liver in MW group was increased to 28.9%, 53.8%, 69.7% and 30.2% of normal group at the 2nd, 4th, 6th and 8th days after the irradiation, respectively, but recovered to the level of normal group at the 16th day. The present results indicated that antiox idative defense systems of rats irradiated microwave was weaken more than that of normal group, which lead to acceleration of lipid peroxidation.