Commercial production of broiler and layer flock is dependent on the immunological status of the birds. Genetically determined immunocompetence and environmental factors are responsible for varying susceptibility or resistance to infectious diseases of chicken. The primary and secondary lymphoid organs are the main components of immune system in vertebrates. understanding age-related immunocompetence by evaluating circulating T lymphocyte population in apparently healthy commercially raised chicken is of direct relevance to developing breeding strategies as well as promoting health measures of the flock. Hence, to bridge the gap in avian immune research with regard to understanding the ultrastructural details of the lymphoid organs and age related changes in T lymphocyte subset population, the present study was carried out with the aim to trigger the interests of the researchers who are keen to venture in this field.