Introduction . In accordance with Russian Federal Program of import substitution of foreign medicines replacement for high-quality Russian drugs in Russia reproduced нydroxycarbamide (HC), which passed preclinical toxicological and pathomorphological testing in comparison with hydrea (HD), producted by Italy.The aim . The aim of present study was the comparative evaluation of HC and HD effect on the internal organs of rats for the clearing up of their identity according to the morphological criterions. Materials and methods. 70 non-inbred male rats, by 10 rats per group, were used. HC and HD were administered to rats oral daily for 5 days in the same total doses correspond with to the 2, 1 and 1 / 2 maximum tolerated dose. In the same regime control rats were oral administered with 1 % starch paste solution. Of animals were removed from the experience on days 3 and 30 after the end of the administration of the drugs. The macroscopic and histological examination of internal organs were perform by routine methods, including fixation of the material in 10 % formalin and staining of sections with hematoxylin and eosin. The histological preparations of the internal organs was analyzed in the light microscope at magnifications of 100, 400, 1000. Results . HС, as well as HD, in total doses of 3000 and 1500 mg / kg at the 3 day after the end of the introduction caused different degrees of similar morphological changes in rat internal organs: moderate hypoplasia in the thymus, bone marrow and spleen, destructive and inflammatory changes in the stomach, duodenum and kidney. At the 30 day after the application of both drugs morphological changes in the thymus, the bone marrow and the spleen disappeared completely, residual morphological changes persisted in the duodenum and kidneys; in the testes of rats – moderate atrophic changes. HС, as well as HD in total dose 750 mg / kg did not cause changes in the internal organs of the rats. Conclusion . Based on the results of macroscopic and histological examination the conclusion about of the identity of the influence of HC and HD on the internal organs of rats was made.