A total number of eighteen day old Hansli chicks and eighteen day old Vencobb broiler chicks were divided into three age groups viz. group I (up to 1 month), group II (1-3 months) and group III (3-6 months) with six birds in each age group. It was revealed that the thymus was surrounded by a capsule and comprised of peripheral darker cortex and central lighter medulla. There was presence of lymphocytes, reticular cells, plasma cells, macrophages, fibroblasts, dendritic cells and erythrocytes in both the cortex and medulla of thymus in both the birds in all the age groups. The spleen was surrounded by a dense irregular connective tissue capsule. The splenic white pulp had lymphocytes of various sizes, dendritic cells, macrophages and blood vessels. The splenic red pulp consisted of splenic cords and venous sinuses. The splenic cords had erythrocytes, reticular cells, lymphocytes of various sizes, heterophils and plasma cells. The wall of the bursa consisted of innermost tunica mucosa, middle tunica muscularis and outermost tunica serosa. The follicle-associated epithelium of the plicae was pseudostratified ciliated columnar type with areas of simple cuboidal cells. There was presence of lymphocytes of various sizes, reticular cells, plasma cells, macrophages, dendritic cells and fibroblasts in both the cortex and medulla of bursal follicles. The collagen, reticular and elastic fibres were reported in different regions of thymus, spleen and bursa of Fabricius in both the birds.