Background: Toxicity of organophosphate insecticides is mainly due to the inhibition of acetylcholinesterase (AChE). However organophosphate insecticides in acute as well as in chronic and subchronic intoxication may lead to oxidative stress causing enhancement of lipid peroxidation and changing the activities of antioxidative enzymes and concentration of non-enzymatic antioxidant. For this reason the aim of the work was to estimate glutathione and hydrogen peroxide levels in the liver, as well as the concentration of total glutathione in serum of rats in subchronic intoxication with chlorfenvinphos. Materials and Methods: The animals received chlorfenvinphos, intragastrically with use of a stomach tube, at a one daily dose of 0.3 mg/kg/day for 14 or 28 days. For biochemical determinations BIOXYTECH GSH-400™ and BIOXYTECH H2O2-560™ Assay kit, OXIS International, Inc., Portland, USA (reduced glutathione and hydrogen peroxide), and Glutathione Assay Kit, Cayman Chemical Company, USA (determination of serum total glutathione level) were used. Results: Chlorfenvinphos administration resulted in a decreased level of reduced glutathione in liver accompanied by an increase in liver hydrogen peroxide and serum total glutathione concentrations. The observed changes were more pronounced after 28 days of intoxication. Conclusions: The common use of organophosphate insecticides results in the environmental pollution, therefore, the decreased liver glutathione level is an additional risk factor for people treated with different medicine (e.g. paracetamol).