The purpose of this work is to describe the structural parameters of the immune system organs in the Mute swan (Cygnus olor). The work was carried out in the laboratory of the Department of Pathological Anatomy and Histology of the Vitebsk State Academy of Veterinary Medicine. The object of the study were the corpses of immature Mute swans, the subject – the organs of the immune system (spleen, thymus, cloacal bursa). It has been established that the topography, macro- and microscopic structure of the cloacal bursa, thymus and spleen do not differ significantly from those of other members of the Aves class. The wall of the cloacal bursa consists of mucous, muscular and serous membranes. The folds of the cloacal bursa are lined with a single-layer multi-row epithelium, and the lymphoid follicles are the functional units of the organ. Macroscopic and histological studies have not found the presence of pathological changes in the thymus, spleen and cloacal bursa (necrosis, atrophy, hyperplasia, etc.), which characterizes them as fully functioning organs of the immune system, capable of fully performing their functions. Also, the paper presents the indicators of micromorphometry of the organs of the immune system of the Mute swans, which on the whole is a generalization of the studies.