Adenomyosis is a nonneoplastic proliforation of uterine glands characterized by multicentric infiltration of endometrial tissues into the myometrium. A female domestic short hair cat with unknown age was referred to local animal hospital in Busan for ovariohysterectomy to prevent the unwanted offspring. At the time of surgery, the uterus was enlarged with multiple nodular protrusion on the serosa. On the cut surface of uterus, elevation of the endometrium and hypertrophied myometrium were observed. Microscopically, the uterus was characterized by severe proliforation of endometrial glands into the lumen and within the myometrium. The intra-myometrial endometrium is circumferentially surrounded by bundles of hypertrophic smooth muscle cells. These endometrial glands had tall columnar epithelium lacking nuclear atypia and mitoses. In our best knowledge, this is the first report of feline adenomyosis in Korea.