The problem of toxocariasis is essential for both human and veterinary medicine. Therefore, the study aimed to determine the effect of fenbenzyl and fenbendazole on the morphological parameters of the blood of dogs, with experimental infestation with the pathogen toxocariasis. The experiments were performed on 18 dogs, two to four months of age, and three groups of six animals were formed in each: control and two experimental groups. Puppies of all groups were experimentally infected with toxocariasis at a dose of 5,000 invasive T. canis eggs per kg body weight. The control group of dogs was as untreated control. Puppies of the first experimental group were fed the drug “Fenbendazole” at a dose of 150 mg per 3 kg of animal weight once a day for three days in a single dose. Puppies of the second experimental group were fed Fenbenzyl at a dose of 350 mg per 3 kg of animal weight once a day for three days. It was found that the use of fenbendazole in infected dogs, the number of erythrocytes and hemoglobin in their blood increased compared with the control group but did not reach physiological values. In the second experimental group of animals treated with fenbenzyl, an increase in these indicators was found throughout the experiment. On days 25 and 30 of the experiment, the number of erythrocytes and hemoglobin fluctuated within physiological values. When prescribing drugs “Fenbendazole” and “Fenbenzyl” found a decrease in leukocytes from 10 days of the experiment. In the second experimental group, the number of leukocytes was more likely to decrease than the control group. Such changes in the blood are due to the antiparasitic effect of the drug “Fenbenzyl” and the cessation of toxins of Toxocara on the bone marrow. It was found that the number of eosinophils, neutrophils, and monocytes in animals was significantly reduced in all experimental groups compared to uninfected, infected dogs. It should also be noted that the number of lymphocytes in the blood of dogs of the experimental groups probably increased from the 15th day of the experiment. On days 25 and 30 of the experiment, an increase in the number of lymphocytes to physiological values was found in dogs treated with Fenbenzyl. Thus, the use of fenbenzyl in the second experimental group of dogs helped restore blood morphological parameters to the level of control, which, in our opinion, is due to reduced immunosuppressive effects of Toxocara on their body, as well as hepatoprotective, immunostimulatory, and antioxidant effects of milk thistle.