The immunomodulatory agent Imunofan (Bionox, Russia) is widely used in clinical practice. It affects the immune and endocrine systems and enhances cell-mediated and humoral immunity. The aim of this study was to investigate the cell profile (lymphoblasts, small, medium and large lymphocytes, macrophages, mitotic cells and damaged cells) in the subcapsular and inner zones of the thymic cortex and thymic medulla of random-bred male albino rats with conspicuous age-related changes after stimulating their immune system with Imunofan. The animals in the experimental group (n = 30) were administered to intramuscular injections of the drug (0.7 mg/kg) on the 1st, 3rd, 5th, 7th and 9th days of the experiment; the controls (n = 30) were administered to the equivalent amount of normal saline on the same days. Rats were decapitated on the 1st, 7th, 15th, 30th and 60th days after the final injection. Thymic sections were studied using Olympus CХ-41 microscope, Olympus SP 500UZ camera (Olympus, Japan) and Morpholog software (Ukraine). Thymic morphology was similar in the experimental and control groups; however, cell profiles were different. On the 7th, 15th and 30th days, lymphoid cells and macrophages prevailed over damaged cells, the number of which decreased (p <0.05). Similar statistically significant trends were found in the inner zone of the thymic cortex. The number of medium lymphocytes was statistically higher on the 7th, 15th and 30th days of the observation, while the number of small lymphocytes was also higher on the 60th day of the observation. The number of damaged cells was significantly lower on the 15th and 30th days (p <0.05). The obtained results indicate conspicuous thymic response in rats with conspicous age-related changes to Imunofan administration, and partial temporary delay of age-related thymic involution.