Medicinal leeches are used for therapeutic purposes in the prevention and treatment of many diseases. Because they have a large amount of biologically active substances in their body. Each of these substances has many therapeutic effects. In natural conditions, they are mostly are fed of blood by wild animals. In laboratory conditions, the blood of domestic animals is mostly used. Currently, medicinal leeches are mostly bred in laboratory conditions. Because there are very few of them in nature. They are listed in the Red Book. Scientists of various specialties are looking for optimal conditions for their life and breeding. That became our research goal. To identify the influence of blood human, domestic animals (pigs and chickens) and small laboratory animals (rats) on the viability and behavior of medicinal leeches Hirudo verbana Carena, 1820 and Hirudo orientalis Utevsky & Trontelj, 2005. According to this, 8 groups of sexually mature animals were formed: 1 and 2 - human blood; 3, 4 - blood of a domestic pig; 5, 6 - blood of domestic chickens; 7, 8 - blood of a non-linear laboratory rat. As a result of the study, it was found that the blood of pigs and chickens is the most suitable for feeding the medical leech for normal life and behavior. Mortality of leeches was observed when feeding on rat and human blood. It should be noted that at the beginning of feeding animals with blood human. The percentage of cannibalism in animals increased.