Light and transmission electron microscopic studies of thymic myoid cells in Nandanam Chicken was done in various age groups ranging from day-old to forty weeks. Thymus is the central lymphoid organ in fowl, provides a complex environment essential for T-cell development and maturation. The thymic gland in chicken was covered by a thin connective tissue capsule. The connective tissue septa divided the gland into lobules. Thymic parenchyma consisted of an outer darker cortex and inner pale medulla. Under light microscope, numerous large cells with eosinophilic cytoplasm were observed in the medulla and also in the cortico-medullary junction, the myoid cells. Number of myoid cells increased as age advances. Under electron microscope, the cytoplasm of the myoid cell showed myofibrils as in skeletal muscle fibre. Cytoplasm also contained few mitochondria, free ribosome and smooth endoplasmic reticulum. Small bundles of unmyelinated nerve fibres were observed in the thymic medulla