Abstract: Pentachlorophenol-induced oxidative stress in liver of crucian carp was studied by comparing crucian carps in the control with those exposed to solutions with pentachlorophenol(PCP) concentration at 0.001 6,0.016 and 0.16 mg·L ^-1 separately for 15 days in SOD,GSH,MDA,NO and NOS in livers of the crucian carps.The results show that the carps in the 0.16 mg·L ^-1 treatment all died on 13th day;that in the 0.001 6 mg·L ^-1 treatment,PCP increased MDA and NO contents in livers of the carps and decreased GSH content,and SOD activity was inhibited whereas NOS activity stimulated;and that in the 0.016 mg·L ^-1 treatment,the effects of PCP on these indexes were more significant than in the 0.001 6 mg·L ^-1 treatment.These data indicate that exposure to PCP may lead to generation of free radicals,depletion of antioxidants and peroxidation of lipids,thus resulting in oxidative stress in livers of the crucian carps.