Abstract. The herbicide propisochlor is widely used in agriculture of Ukraine. Its intensive usage is potentially dangerous due to residues in agricultural products, ecosystems, as well as effects on animals’ and humans’ organisms. This fact necessitates the study of its toxicological properties. Aim. To study the propisochlor carcinogenicity in a long-term experiment on male rats. Materials and Methods. The experiment was performed on Wistar Han male rats. There was investigated a sample of 95 % technicalgrade propisochlor, administered to animals intragastrically at doses of 20 and 200 mg/kg of body weight for two years. At the 52ndweek-term, a group of animals was selected to study the propisochlor toxicity. Carcinogenicity was assessed at the 104th week. Results. The toxic effect of propisochlor on the rats’ bodies was revealed in weight loss affected by a 200 mg/kg dose, starting from the 29th week of testing. According to the analysis results of the clinical biochemistry, it was found that propisochlor at a dose of 200 mg/kg at the 52nd week of exposure tended to decrease the activity of ALT and AST. Histologically at the terminal stage at a dose of 200 mg/kg in rats the hepatocellular necrosis with associated focal hemorrhages were detected, which confirmed hepatotoxicity; and in the thyroid gland it was found the increase of nodular follicular-cell hyperplasia cases. Propisochlor did not affect the survival and life expectancy of rats, did not increase the number of animals with tumors, did not affect the multiplicity of newgrowth, did not change the ratio of benign and malignant tumors, and also did not reduce their latency, the dose-effect relationship was not observed. Conclusions. Propisochlor, 95 % technical-grade generic, did not show the carcinogenic effects in a two-year experiment in male rats. NOAEL was identified according to general toxicological criteria and it was 20 mg/kg. Key Words: propisochlor, carcinogenesis, toxicology, Wistar Han male rats, long-term experiment.