Chlorfenvinphos is an organophosphate insecticide widely used alone or in combination in Poland. In the present study, the influence of chlorfenvinphos on the activity of mitochondrial antioxidative system as well as hydrogen peroxide concentration was examinated. The experiments were conducted on male Wistar rats of 180±20g body weight. The animals were divided into two groups: the control group, which received oil intragastrically by stomach tube and the experimental groups, which received oil solution of chlorfenvinphos in doses of 0.02 LD₅₀, 0.1 LD₅₀ or 0.5 LD₅₀. After 1, 24, 48 hours the livers were quickly removed. Liver mitochondria were isolated as described elsewhere. Glutathione peroxidase, superoxide dismutase, isocitrate dehydrogenase activity as well as reduced glutathione and hydrogen peroxide concentrations were determined in liver mitochondria using BIOXYTECH Assay kits produced by OXIS International, Inc., Portland, USA. The results of this work indicate that chlorfenvinphos induces oxidative stress to rat liver mitochondria. In acute chlorfenvinphos intoxication, we demonstrated that the key role in the oxidative mitochondrial damage play MnSOD and GSH pool, as well as accumulation of hydrogen peroxide.