In the experiment, it was proved that the use of milk Thistle oil prevents the development of hepato-toxic action of carbon tetrachloride in dogs. The use of herbal drug prevents the activation of processes of lipid peroxidation, which was manifested by the decrease in the level of malondialdehyde in the serum of the animals treated with carbon tetrachlo-ride. In the group of animals treated with thistle oil on the background of administration of xenobiotic, on the 10-th day of the experiment, the MDA level in the blood serum was by 30.6 % lower than in the animals receiving only xenobiotic. Stabilizing effect of milk thistle oil revealed toxic hepatitis of dogs, which was manifested by normalization of the con-tent of aminotransferases in blood serum. ALT ac-tivity in animals, taking both herbal drug and model xenobiotic on the 10-th day of the experiment was by 28.9 % lower (P<0.01) and the activity of AST was by 33.2 % (P<0.05) than in dogs who received only xenobiotic. Milk thistle oil on the background of using carbon tetrachloride prevented the decrease in the level of albumin in the blood serum: on the 10-th day of the experiment 16.6 % (P <0.05), and alpha-globulins were by 36.8 % (P <0.05), this was due to the normalization of protein-synthesis almost every day in the liver. The content of gamma-globulin on 10-th day of experiment in dogs receiv-ing both hepatoprotective and xenobiotic below 14 % (P<0.05) than in the animals treated only with xenobiotic, which indicated the prevention of in-flammatory response in the stroma of the liver. Thus, thistle oil prevents the process of lipid perox-idation, the development of cytolysis of hepatocytes and stimulates protein-synthetic function of liver at toxic hepatitis of dogs.