A 50-year-old peri-menopausal woman presented with hard palpable mass on her lower abdomen and anemia from heavy menstrual bleeding. Ultrasonography showed a 13x12 cm sized hypoechoic solid mass in pelvis and a 2.5x2 cm hypoechoic cystic mass in uterine endometrium. Abdomino-pelvic computed tomography revealed a hypodense pelvic mass without enhancement, suggesting a leiomyoma of intraligamentary type or sex cord tumor of right ovary with submucosal myoma of uterus. Laparoscopy revealed a large Sertoli-Leydig cell tumor of right ovary with a very rare entity of intra-endometrial uterine leiomyoma accompanied by adenomyosis. The final diagnosis of ovarian sex-cord tumor (Sertoli-Leydig cell), stage Ia with intra-endometrial leiomyoma with adenomyosis, was made. Considering the large size of the tumor and poorly differentiated nature, 6 cycles of chemotherapy with Taxol and Carboplatin regimen were administered. There is neither evidence of major complications nor recurrence during 20 months' follow-up.