In basic sciences, laboratory animals have a special role in investigations. In this study, the adrenal of three adult female guinea pigs and hamsters were studied. The left adrenal was larger than the right in two species. In hamster, it was in the cranial pole, and in guinea pig, it was in the craniomedial pole of the kidney. In guinea pig, the right and left glands were bean shape and in hamster, egg shape. This gland was covered by a capsule without muscle fibers in guinea pig and hamster. The peripheral cortex in hamster was divided into three zones and in guinea pig, four zones. Zona glomerulosa was composed of arcuate cords in guinea pig and clusters in hamster. The foamy cytoplasm of fasciculate in guinea pig was more than hamster. There was also a lot of lipofuscin in cytoplasm of reticularis in the two animals, especially in guinea pig. The medulla in guinea pig was long and in hamster was egg-shaped. In guinea pig, reticularis cells penetrated into medulla and invagination of cortex also was obvious in medulla of this species. In chromaffin reaction, the less electron-dense granules were epinephrine and the dense granules were norepinephrine cells

Keywords