The experiment was conducted to elucidate the histomorphology of thyroid gland of prepubertal, pubertal and castrated adult indigenous bulls (Bos indicus) using Hematoxyline and Eosin (H&E) during July 2013 to June 2014. Twelve bulls of three age groups namely prepubertal (below 1 year of age, n=4), pubertal (1.5 to 2.5 years, n=4) and castrated adult (above 4 years, n=4) were selected in this study. Thyroid glands of slaughtered bulls were collected for histological studies. The thyroid gland was found to cover by a thick connective tissue capsule consisted of dense collagen fibers having two layers, outer and inner layer. The follicles consisted of follicular epithelium and intrafollicular colloid substances. Shapes of the follicles were seen round, oval, pentagonal or hexagonal and irregular in appearance. In prepubertal group, most of the follicles were smaller. In pubertal group, most of the follicles were larger in sizes including some smaller follicles. Significant differences were found in the follicular diameters of the prepubertal from the pubertal bulls. Castrated bulls showed larger inactive follicles with few smaller follicles. Colloid was more homogenous, predominantly eosinophilic by H&E staining in most active follicles. Follicular epithelium become simple squamous to low cuboidal in prepubertal bulls, low cuboidal to columnar in pubertal bulls and squamous epithelium in castrated adult bulls. Para follicular cells were frequently found beneath the basal lamina in prepubertal bulls, but in pubertal and castrated bulls a fewer or no parafollicular cells were found. Finally, thyroid glands were found to undergo age related changes and histological features indicated the functional status of the thyroid gland.