The current study was performed to investigate age-dependent immunoexpression and localization of somatotropin in the pituitary gland. Twenty adult Wistar rats (fifteen females and five males) were housed; four animals per cage with observation of pregnancy. Samples from pituitary gland were collected from different ages of male offsprings. Tissue specimens were processed, and stained with Hematoxylin and Eosin (H&E), special stain and immunohistochemical technique. Sections were divided into four stages. H&E results showed that at stage I, acidophils were the most distinguished cells; but basophils were difficult to be seen then appeared at stage II. Special stain results showed increasing in somatotrophs number from stage I to stage III then decreased at the last stage. Immunoexpression of somatotropin in pars distalis showed that somatotrophs were numerous and uniformly distributed at the first three stages then they were restricted in clusters at the last stage.