Ovarian adult-type granulosa cell tumors are often associated with endometrial hyperplasia or even uterine cancer. Herein, we present a case report of a 65-year-old female patient who had undergone curettage of the uterine cavity several times due to abnormal and irregular uterine bleeding. Owing to recurrent episodes of vaginal bleeding as well as ineffective pharmacological treatment of simple endometrial hyperplasia without atypia, the patient underwent a laparoscopically-assisted vaginal hysterectomy. Owing to an enlarged right ovary with bluish color, intra-operative pathological examination was immediately performed. Surprisingly, an ovarian adult-type granulosa cell tumor was diagnosed, and the surgery was extended to pelvic lymphadenectomy and omentectomy. Immunohistochemical staining with selected antibodies (Arginase 2, Nidogen 2, BAF250a/ARID1A, GPR30, SF-1/NR5A, and 1LRH-2E1/NR5A2) was also performed. In conclusion, in cases of recurrent vaginal bleeding concomitant with endometrial hyperplasia, the existence of rare ovarian tumors connected with extensive estrogenic stimulation must be taken into account. Immunostaining with selected antibodies (Arginase 2, Nidogen 2, ARID1A, or GPR30) may help elucidate the possible molecular mechanisms associated with the BAF250a/development of various ovarian/endometrial abnormalities.