Abstract Adrenal gland is one of the most important glands of the endocrine system located in the anterior pole of kidney, and it secrets important hormones that role in carbohydrate, water and electrolyte metabolism and maintain the blood pressure in birds. Since there was little information regarding histology and stereology of adrenal, this study was conducted. For this purpose, 8 animals were prepared to study the histology and stereology of Guinea fowl ٬s adrenal. The birds were killed and both of adrenals were removed and immersed in buffer formalin10%. Then, tissue sections were prepared from the samples and were studied after staining with hematoxylin and eosin and green masson 's trichrome. Histological results showed that adrenal was composed of three zones. The subcapsular layer consisted of a thin layer of medullary cells. Peripheral layer consisted of cortical and medullary cells that cortical cells were dominant and medullary cells were in to small groups among them, and central layer consisted of cortical and medullary cells that medullary cell were dominant. Sinusoids and ganglion cells were observed in all areas of adrenal. With the aid of stereological technique, the percentage of different parts of the adrenal was determined.In the right adrenal cortex was 69/34%, medulla 20/83%, capsule 5% and sinusoids were 4/83%. In the left adrenal cortex was 71/16%, medulla 20/16%, capsule 4/68% and sinusoids were 4%. Statistical analysis showed that in both glands cortex has the most volume and after that was medulla and there was no significant difference between two glands.

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