Cattle fasciolosis is quite widespread in the world, including in Ukraine. Animal blood proteins, being in close functional connection with proteins of various tissues, reflect the changes that occur in the tissues and organs of the body during disorders of their metabolic processes caused by pathological factors. The aim of the study was to investigate the level of total protein and its fractions in the blood of cows in experimental fasciolosis. 12 cows of 4–5 years of age, black-spotted breed, were selected for experiment, out of which 2 groups were formed, six animals in each. Animals in the control group were clinically healthy. Animals of the experimental group were experimentally infected with adolescents. During the research, the rules of compulsory experiments were followed - selection and keeping of analogue animals in groups. The cows' diet was balanced in terms of nutrients and minerals. In the study of protein-sensitizing function of the liver of cows, it was found that during fasciolosis invasion, the content of total protein decreased by 13.8 %. These changes were due to a decrease in albumin and an increase in globulins. Thus, in fasciological invasion of cows, the level of albumin in the serum decreased by 24.4 %, and the level of globulins increased by 7.9 %. The value of the albumin / globulin ratio in the blood of infested cows with the causative agent of fasciolosis is quite indicative. It was found that the albumin-globulin ratio in the blood of cows of the experimental group was probably lower compared to the control group of animals. This value of the coefficient, of course, indicates the suppression of protein-synthesizing function of the liver in these periods of research. In the future it is planned to investigate the functional state of the liver of cows with experimental fasciolosis.