The indiscriminate usage of various types of pesticides in the modern world has led to serious environmental hazards, threatening the survival of mankind. The present study was undertaken to evaluate the influence of cypermethrin, a widely used synthetic pyrethroids pesticide, on antioxidant enzymatic defense system and lipid peroxidation in different organs of fresh water fish, Cyprinus carpio. Fishes were exposed to sub lethal concentration of cypermethrin for three different durations, 7, 14 and 21 days and were sacrificed 24 hrs after the exposure. The enzyme estimations were performed in gills, liver and brain by standard spectrophotometric methods and the values were compared with the controls. The activity of catalase was increased in gills and brain and decreased in the liver. The activity of superoxide dismutase was increased in gills and liver in all the durations and decreased in the brain. Glutathione peroxidase was decreased in all the three organs. In all the three organs, glutathione reductase and glutathione-s-transferase activity was significantly reduced. A significant increase in lipid peroxidation was observed in the liver, gills and brain of the fish following exposure to cypermethrin. In all the three organs studied the influence of cypermethrin was found to be exposure of time dependent.