Morpho-functional changes in the organs of the male reproductive system are usually associated with injuries, infectious diseases, age, lifestyle, the presence of bad habits (abuse of alcohol, drugs), the influence of environmental factors, etc. However, the action of natural toxins, in particular those that are components of animal venoms, including the venoms of snakes and vipers, is no less important. The aim of the research is to study the features of the microscopic structure of the testis of rats under the influence of Vipera berus berus venom. Experimental studies were carried out on white non-linear male rats. Animals were conditionally divided into two groups – control and experimental, 10 individuals in each. Experimental rats were injected intraperitoneally with a semi-lethal dose (LD50) (1.576 mg/g-1) of Vipera berus berus venom in physiological solution. Animals of the control group were injected intraperitoneally with only saline solution. Rats were removed from the experiment 24 hours after exposure of the venom, anesthetized by cervical dislocation. Testis samples were taken for microscopic examination. Fixation of the material and preparation of paraffin blocks were carried out according to generally accepted methods. Staining of histological preparations of the testis was carried out with hematoxylin and eosin. Histological preparations were studied using a SEO SСAN light microscope. Administration of Vipera berus berus venom to rats leads to the development of pathogistological changes in the parenchymal elements of the testis of animals, among which desquamation and disorganization of all stages of spermatogenic cells development, disruption of spermatogenesis processes were the most pronounced. Spermatogenic cells of the seminiferous tubules of the testis were distinguished by changes in morphology and location, lost the regularity of their placement, and their number decreased. The cells detached from the basement membrane and did not form a continuous layer. A characteristic feature was the presence of clusters of erythrocytes in the lumen of the seminiferous tubules, which may indicate the development of hemorrhagic complications. In addition, an increase in the number of Leydig cells was detected, which is probably the cause of changes in the hormonal regulation of the organ's function.