Abstract: Effects of Cd²⁺ on peroxidase systems(POD)in organs of grass carp,like liver,kidney and gill were studied with the hydrostatic biological test method.Results show that within the 7 days of experiment period,under low Cd²⁺stress,the activity of POD in the liver and kidney tissues decreased first then increased and decreased once again as time elapsed,while under high Cd²⁺stress,the activity of POD in the liver was significantly inhibited through all the 7 days of experiment period (P<0.05).Under high Cd²⁺stress,POD in kidney was firstly reactivated in a short time,but was soon inhibited significantly(P<0.05).However,under Cd²⁺stress,the activity of POD in the gill first increased and then decreased with time during the 7 days of experiment priod,and was obviously lower than that in liver and kidney.