Herein, a rare case of ovarian granulosa cell tumor, presenting as Meigs' syndrome, with elevated carbohydrate antigen 125 (CA125), is reported. A 69-year-old woman was admitted for the investigation of abdominal fullness and dyspnea. A preoperative examination revealed a huge pelvic tumor and an abdominopelvic magnetic resonance image (MRI) assumed ovarian cancer. A chest computed tomography (CT) scan revealed pleural effusion. A laparotomy confirmed the huge mass to be an ovarian tumor. A total abdominal hysterectomy (TAH), with a bilateral salpingo-oophorectomy (BSO) and partial omentectomy, was performed. Although short-term intrathoracic drainage was required, the hydrothorax and ascites rapidly resolved in the postoperative period.