Organophosphate compounds are nowadays the most frequently used pesticides. For these insecticides, the primary target is acetylcholinesterase and for this reason the main clinical effect of acute intoxication with organophosphate insecticides involves an irreversible inhibition of the activity of this enzyme. However, in the chronic or subchronic exposition oxidative stress has been reported as the main mechanism of its toxicity. The present study investigated the effect of three low doses (0.2, 2, 5 mg/kg bw) of chlorpyrifos for 14 or 28 days on serum liver enzymes and on oxidative stress parameters in the liver of rats. Chlorpyrifos treatment resulted in aminotransferases and alkaline phosphatase increase after 14 days (higher doses) and 28 days (all doses) treatment together with changes of antioxidative enzymes activities and reduced glutathione and malonyldialdehyde level in the liver. The enhancement of lipid peroxidation is temporary, reaching a peak after 14 days and decreasing after 28 days of treatment. Based on the experimental findings of this study the temporary liver injury caused by oxidative stress has been shown. The disturbances in the liver antioxidative status and increased liver membrane permeability may appear in case of doses near to the accepted human daily intake.