Abstract: With variant concentrations of cadmium (Cd) (7.25mg/L,14.5mg/L,29mg/L,58mg/L and 1.6mg/L) and treating times (24h,48h,72h and 96h) disposed on freshwater crab, Sinopotamon yangtsekiense,the activities of Superoxide dismutase (SOD) and Glutathione Peroxidase (GSH2Px) were investigated by acute toxicity. In the range of exposure dosages,the activities of SOD and GSH2Px in these two tissues were found going up and then down with the increasing concentration of Cd and treating time. However,the content of Maglonydiadehyde (MDA) was continuatively improved. When explored at 14.15mg/L of Cd for 48h,the SOD activity of the two tissues amount to the highest,being(34.123 ±0.993) U/mg protein and(29.340 ±1.802) U/mg protein, respectively in hepatopancreas and gill,and values were both significant. However,the GSH2Px activities in hepatopancreas,when treated by 7.25mg/L of Cd for 48h,attained to the maximum,and it was in gill by 14.5mg/L for 24h.More2 over,the activities of SOD and GSH2Px potentially decreased with the up of Cd concentration and treating time,and then dropped to the lowest at 1.6mg/L of Cd. Ratio of GSH2Px/SOD is useful tool as index of antioxidant level. It was revealed that the ratio of GSH2Px/SOD in tissues and treated Cd concentration plus time was converse.Briefly,the experimental results suggested that the variations on the enzyme activity and the MDA content may sensitively indicate the toxicity of Cd as well as the inhibition effects of enzymes to it.Besides,the possible mechanism was also analyzed and discussed.