Meigs' syndrome is a fibroma associated with ascites and/or pleural effusion. Ovarian fibromas are uncommon sex cord-stromal neoplasm. Most of them are benign, and often found in postmenopausal patients. Abdomino-pelvic computerized tomography (APCT) scan shows hypodensity or isodensity of the tumors. However, the preoperative diagnostic rate is rather low due to its low incidence, diverse clinical symptoms, and the great differences existing in tumor size and shape. It is therefore often misdiagnosed as uterine myoma. When the tumor size is large, with ascites, and elevated cancer antigen 125 (CA125) level, it is also misdiagnosed as malignancy. The authors report a 57-year-old woman who presented with palpable giant pelvic mass. APCT showed a heterogenous giant mass measuring 17×17 cm with moderate amount of ascites. No pleural effusion was detected on chest X-ray. CA 125 level was normal. The patient underwent laparotomy during which a mass measuring 17×17 cm was detected in her right ovary with 500 ml of ascites. Histology showed ovarian fibroma. The authors performed total abdominal hysterectomy with bilateral salpingo-oophorectomy. Postmenopausal woman with ovarian tumor, ascites may indicate malignancy, but Meigs' syndrome must be considered as differential diagnosis.