Abstract: Using a static toxicity experiment method,the effects of monocrotophos(MCP) on CAT and Na⁺,K⁺-ATPase activities in the gill,liver and kidney of Monopterus albus were studied.The results showed that at((20±2) ℃,) the LC50 of MCP for 96 h were 3.27(mg/L) to Monopterus albus.After the 96 h MCP exposure of 0.25,0.50,1.00 and 2.00(mg/L,) the CAT activity in the three tissues increased at the mass concentration of 0.25 and 0.50(mg/L,) but decreased at 1.00 and 2.00(mg/L.)In all the three tissues,the statistic significant increased and decreased alteration was at 0.25(mg/L)(P<0.05) and 2.00 mg/L(P<0.05),respectively.The Na⁺,K⁺-ATPase activities in the three tissues were all depressed with the increasing MCP exposure concentrations.The Na⁺,K⁺-ATPase activity in gill was more susceptible than kidney,but in the liver it showed no significant alteration.