The article presents the results of determination of acute and subacute toxicity of the drug “Tilovet 20 %”, which was made on the basis of tylosin tartrate. In result of the conducted researches, it was found out, that LD50 of the drug “Tilovet 20 %” by intramuscular injection to white mice (calculated by the method of G. Kerber) is 10000 and mg/kg, and for white rats – 9583.33 mg/kg. Long-term use of the drug in a therapeutic dose caused a tendency to the decrease of hemoglobin concentration, amount of erythrocytes, platelets, hematocrit value, mean corpuscular hemoglobin (MCH), mean corpuscular volume (MCV), content of the total protein, creatinine level, ALP activity on the background of a slight an increase of amount of leukocytes, urea level, AST and ALT activity compared to the values of the control group. The use of the drug in a dose that is 10 times higher than the therapeutic, caused a probable decrease of hemoglobin concentration by – 6.6 % (P < 0.05), platelet count by – 32.5 % (P < 0.05), mean corpuscular hemoglobin (MCH) by – 4.2 % (P < 0.05), mean corpuscular hemoglobin concentration (MCHC) by – 1.5 % (P < 0.1), hematocrit value by – 4.95 %, and total protein content by – 10.7 % (P < 0.05), on the background of a slight an increase of amount of leukocytes by 5.3 %, ALP activity by – 17.5 %, compared to the values oft he control group. Therefore, all of the above may indicate to the suppression of hematopoietic processes and a decrease in the protein-synthesizing function of the liver.