The present experiment analyzed the effect of atrazine and chlorpyrifos single or joint exposure on the activities of antioxidant enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) at different time periods and concentrations in Salamander (Hynobius leechii) tadpoles from northeastern China. With the increase of exposure time and elevation of concentration in each treatment group, the activities of SOD, CAT and GSH-PX decreased significantly, while the level of MDA increased significantly (shown in Fig. 1, 3, 5), indicating that exposure of H. leechii tadpoles to atrazine and chlorpyrifos, single or joint, impairs antioxidant system and produces a toxic effect. After 21 days of exposure, the activities of various enzymes in the low or moderate concentration group was not different as compared to their counterparts at the end of revovery, while the high concentration group showed significant improvement of enzyme activities after recovery (shown in Fig. 2, 4, 6).