The capacity of T cells to recognize and mount an immune response against tumor antigens depends on the large diversity of the T-cell receptor (TCR) repertoire generated in the thymus during the process of T-cell development. However, this process is dramatically impaired by immunological insults, such as that caused by tumorinduced thymic involution. The aim of study was to investigate the possibilities of zinc supplementation to prevent thymic involution and check functional activity of thymocytes during the growth of transplantable tumors in mice. Inbred C3HA mice received zinc sulfate after subcutaneous inoculation of hepatoma 22a. On day 21 thymuses were extracted and evaluated for proliferation and apoptosis of thymocytes and zinc content in the thymus. Also zinc content in serum blood samples, thymus status and parameters of tumor growth were evaluated. Proliferation (cell cycle analysis) and apoptosis were investigated by flow cytometry. Level of thymus zinc was evaluated using the method of atomic absorption spectrometry. Biochemical methods were used to estimate catalase and Cu,Zn-SOD activity in thymus homogenates. During tumor 22a growth weight and cellular content of the thymus were decreased by 3 times and endogenous zinc content in samples of blood serum was decreased by 1,9 times and apoptosis in thymocytes increased by 2,5 times, while the percentage of cells in the S phase decreased. Oral zinc sulfate increased thymus weight and cellularity as well as serum zinc. It normalized thymocyte proliferation and decreased apoptosis. As a possible mechanism of action, we studied the influence of zinc supplementation in two anti-oxidative defense enzymes. Oral zinc supplementation prevents thymic involution through normalization of thymocyte proliferation and decreased apoptosis. We suggest that zinc administration may be considered as a prospective strategy for thymus reconstitution in oncology patients, especially during treatment with checkpoint inhibitors.