To explore the effects of cadmium(Cd2‘)exposure on the antioxidant enzyme activity of the hepatapancreas, freshwater crabs Sirtopotamon yangtsekiense were exposed to Cd2+(7.25mg/L, 14.5mg/L, 29mg/L, 58mg/L, 116mg/L)for 24, 48, 72 and 96 hours. The activities of antioxidant enzymes were investigated including superoxide dismutase(SOD), catalase (CAT), glutathione peroxidase(GPX), GSSG-reductase(GR)and glutathione S-transferase(GST), and the GPX/SOD, GR/GPX, CAT/SOD ratios, as indicators of antioxidant properties. Results showed that the activities of SOD, CAT and GPX increased initially and decreased subsequently. but GR and GST activities remained almost unchanged. The changes in antioxidant ratios of GPX/SOD, GR/GPX and CAT/SOD indicated that, following the increase of concentration of Cd2+ and duration of treatment, significant cellular injuries were caused in the-hepatapanereas of S. yangtsekiense due to the oxidative stress. We conclude that the changes of the indicators(SOD, CAT, GPX as well as GPX/SOD, GR/GPX, CAT/SOD ratios)may exquisitely reflect the oxidative stress in an aquatic animal induced by Cd2+and the toxicity of it[Acta Zoologica Sinica 53(6): 1121-1128, 2007].