The aim of the study was to investigate the effect of toxocariasis invasion on protein-synthesizing function and functional state of the liver of dogs. For experimental studies, 12 dogs aged from two to four months were used and two groups of six animals were formed in each: control and experimental. Puppies of the experimental group were experimentally infected with the pathogen toxocariasis at a dose of 5,000 invasive eggs of T. canis per kg of body weight. The control puppies were clinically healthy. Protein-synthesizing function of the liver of dogs in experimental toxocariasis was studied by the level of total protein and its fractions. It was found that on the 25th day of the experiment the level of total protein in the blood of the experimental group of dogs was 56.9 ± 1.47 g/l, while in the control group – 63.8 ± 2.92 g/l. The lowest level of the studied indicator was on the 30th day of the experiment in the blood of the experimental group of dogs, where it decreased by 9.6 %. The results of a study of protein fractions in the blood of dogs infested with toxocara showed that the percentage of albumin is likely to decrease. However, in the blood of infected dogs in this period of research there was a probable increase in globulin levels. The study of the effect of toxocariasis invasion on the activity of enzymes in blood serum is a test for the morphological and functional state of tissues and organs. Based on the studies, it was found that with the development of toxocariasis invasion in dogs there is an increase in alanine aminotransferase in their serum. On the 25th and 30th day of the experiment, the activity of the enzyme in the serum of infected dogs was the highest, where compared with the control group of dogs, the activity of ALT increased by 51.2 and 59.1 %, respectively. Similar changes in activity were observed in the determination of aspartate aminotransferase, where, respectively, on the 15th, 20th and 25th day of the experiment, the activity of AST in the serum of infected dogs increased by 19.3, 27.5 and 39.1 %.