The mandibular glands of the Chinese hamster were examined by light and electron microscopy. The mandibular acinar cells were noted to be categorized in a seromucous type, because the acinar cells stained slightly basophile and moderately positive for periodic acid-Schiff (PAS) and alcian blue (AB) reactions and the intercellular canaliculi were detected in the cells. The acini were composed exclusively of light cells containing various secretory granules. The acinar cells exhibited a sexual dimorphism; in the female AB staining was more intense, and also the granules having the matrix of a fine hair-like material were more numerous than in the male. Intercalated duct cells were composed exclusively of light cells and contained round and polygonal granules. The striated ducts consisted of two distinct portions, the secretory and typical striated portions without secretory granules. The epithelial cells of secretory portion were columnar in shape and contained acidophile granules which gave a strongly positive PAS reaction, and comprised light and dark cells containing secretory granules varying in size and density. The epithelium of typical striated portion was composed of both light and dark cells containing fine vacuoles and vesicles, but no secretory granules. No sexual dimorphism was detected in the striated duct.