Objective. The aim of the study was to research the toxicity of L-asparaginase Was79 in rabbits. Materials and methods. Chronic toxicity of L-asparaginase Was79, obtained by modification of native enzyme Wolinella succinogenes in Research Institute of Genetics and Selection, was performed in male and female Russian chinchilla rabbits. L-asparaginase was injected intravenously at the 1 and 5 therapeutic dose (15 x 100 IU/kg or 15 x 500 IU/kg with 24-h interval). The following parameters were tested: body mass, clinical and biochemical blood tests, urinalysis, electrocardiography, pathomorphological evaluation of internal organs. Resutls. The results of the study suggest that the treatment with L-asparaginase Was79 does not influence on the function of heart and kidneys, but damages their structure. Loss in body mass, diarrhea and alteration of stomach and intestine mucosa could be interpreted as evidence of gastrointestinal toxicity. Hematological toxicity was exhibited as a decrease of total leukocyte count, lymphocyte and neutrophils count level in peripheral blood and atrophy of lymphoid tissue of the spleen, thymus and lymph nodes. Elevation of total and direct bilirubin in serum and histopathological findings in liver were found in groups treated with both high and low doses of Was79. Conclusion. Most of these abnormalities were reversible and dose-dependent.