A 13-years and 8-months old Jindo dog showed vomiting and pale red vulvular discharge. At necropsy, the uterus was swollen and endometrium was diffusely thickened by numerous protruding cysts which measured approximately from 0.5 to 1 cm in diameter. On sectioning the cysts exuded pale red watery fluid. histologically the endometrium was thickened and characterized by mild to moderate edema congestion and hemorrhagic foci. The cystic endometrial glands were lined by a single layer of flattened cuboidal or vacuolated columnar epithelium. Occasional dilated glands had traversed through the submucosa into the myometrial region. Afew mixed inflammatory cells infiltrated in the lamina propria. Bacteriologically Escherichia coli was isolated from the uterine contents. Gross and microscopic finding were consistent with cystic endometrial hyperplasia.