The article presents the therapeutic efficacy of Biozinc in the treatment of cattle with serous mastitis. The authors revealed a decrease in the number of somatic cells in milk in the experimental group of cows to 170 thousand, which corresponds to the milk from a healthy animal. Cows in the experimental group showed a positive trend in milk quality. Five cows had watery milk. Positive changes in milk quality were evident 12 hours after the first injection in the form of a reduction in flake secretion from the affected quarters. Milk was watery in all cows of the experimental group by the third day, without flakes and white color. The authors note a positive trend during disease treatment by the end of the first day of treatment in both test groups. Complete recovery was noted in ten animals, which was 100%, in the experimental group, which were treated with Biozinc. Complete recovery occurred after 3.00±0.15 days. The therapeutic efficacy was 100%. In the control group, seven cows (70%) recovered. A hematological examination revealed a 15.52 g/l (18.1 %) increase in hemoglobin level in the experimental group of animals and a 0.88 x 1012/l (P<0.05) increase in erythrocyte count. Through serum biochemical studies, the authors found that cows with serous mastitis showed changes in such parameters as protein, bilirubin, alanine aminotransferase (ALAT), and aspartate aminotransferase (ASAT). Cows in the experimental group showed a 21.5% (P<0.01) decrease in protein content after treatment. The values of ASAT in the control group decreased by 35.2%, and in the experimental group - by 42.6%. The values of ALAT also tended to decrease by 38.7% in the control group and by 48.6% in the experimental group (P<0.001).