Malathion is an organophosphorous insecticide widely used in agricultural and non-agricultural purposes in India, Fishes were sampled, acclimatized and kept treated (0.5 ppm) with malathion and untreated with malathion under observation for 4 days. At day 4, lipid peroxidation activity and superoxide dismutase level increased significantly in treated group as compared to the control. On the other hand, glutathione peroxidase and glutathione reductase activity decreased on treatment with malathion. These results suggest that malathion induces oxidative stress, affects the antioxidant defense system and can cause physiological disturbances that reduce the health and survival of exposed fish.The aim of this study is to assess the adverse effect of malathion on Channa punctatus, in relation to oxidative stress leads to depletion of defences in intestinal macrophages.