Struma ovarii is an uncommon highly specialized ovarian teratoma that accounts for less than 5% of mature teratomas. It is composed predominantly of mature thyroid tissue. Thyroid tissue is observed in 5%-15% of teratomas; however, to qualify as a struma ovarii tumor, the thyroid proportion must comprise more than 50% of the overall tissue. The combination of pseudo Meigs'syndrome and elevation of CA 125 with struma ovarii is a rare condition that can mimic ovarian malignancy. The majority of strumas are benign, however occasionally malignant transformation may be seen. We have reported a case of benign struma ovarii that presented with the clinical features of advanced ovarian carcinoma: complex pelvic mass, gross ascites, bilateral pleural effusion, and markedly elevated serum CA 125 levels. The patient underwent total abdominal hysterectomy and bilateral salpingo oophorectomy. Ascites and pleural effusion resolved completely, and the CA 125 levels have returned to normal following surgical excision. Patients with pseudo-Meigs’ syndrome may present a diagnostic problem as they masquerade as carcinoma with malignant effusions. In addition, the coexistence of struma ovarii and pseudo-Meigs’ syndrome is a very rare event. We emphasize by this report that, despite its rarity, a differential diagnosis of struma ovarii should be included for an ovarian mass.