The activity of antioxidant enzymes — superoxidedismutase (SOD), catalase and glutathionetransferase, and also the level of low molecular weight antioxidants — vitamin E and ascorbic acid in the liver subcellular fractions of rat with transplanted of Guerin’s carcinoma it was investigated. It is shown that in the liver of tumor-bearing rats in the logarithmic phase of oncogenesis increases the activity of the components of the enzymatic link of the antioxidant system (AOS) and the content of vitamin E with a simultaneous decrease of ascorbic acid. The AOS depletionis expressed by a decrease of antioxidant enzymes activity and a decrease the level of low molecular weight antioxidants in the stationary phase of oncogenesis in the liver cells of tumor-bearing rats. It was found that laser irradiation of rats in the area of tumor growth reduces its effect on liver AOS, which is manifested by increased activity of SOD, catalase and vitamin E content in the stationary phase of Guerin’s carcinoma growth in the body.