Abstract: This study investigated the effect of sublethal concentration of malathion on the lipid peroxidation and various enzymes in mice liver, brain and serum. Mature mice were exposed to different doses of malathion and sublethal dose was calculated (80.6 mg kg-1 b.wt. day-1). Two groups of mice were made, first group is control and second experimental. Experimental group was again divided into five subgroups which were exposed to malathion for different time period (2, 4, 8, 15 and 30 days). On dissections, various biochemical estimations such as Aminotransferase (ALT), Aspartate aminotransferase (AST) Malondialdehyde (MDA) and Glutathione-S-transferase (GST) were performed for each exposure period in triplicate. It was found that malathion caused the oxidative stress in different tissues of mice. The maximum period of exposure was up to 30 days. The degree of lipid peroxidation increased in ascending order up to 30 days of exposure period. These findings indicates that the continuous and prolonged exposure to sublethal dose of malathion resulted in induction of lipid peroxidation in mice and alters the activity of enzymes like alanine ALT, AST and GST.