A three-year-old Russian Blue female cat was presented for long-standing infertility and recent development of male behavior. From one to three years of age, the cat had been bred, however, pregnancy never resulted. Abnormal enlargement of the uterus and ovaries was observed by abdominal sonography and radiography. An ovariohystectomy was performed. In the uterus, adenocaricnoma lesions were found and characterized microscopically by replacement of the endometrium with a population of large polyhedral cells with a tubulopapillary or nested arrangement and a supporting fibrous stroma with minimal vascularization. In addition, the pedunculated mass was diagnosed as leiomyoma, which was continuous with the myometrium, composed of closely packed sheets of spindle cells embedded in vascularized stroma, and covered with a discontinuous endometrial epithelium. The ovarian neoplasm was diagnosed as an ovarian interstitial cell tumor. Based on the histopathological characteristics, this case was diagnosed as a simultaneous occurrence of an ovarian interstitial-cell tumor and uterine adenocarcinoma and leiomyoma in a female cat. To the best of our knowledge, this report represents a rare case of multiple tumors in the genital organs of a cat.