Mixed epithelial ovarian carcinomas are extremely rare and comprise less than 4% of all malignant ovarian tumors. We report a 61-year-old postmenopausal woman with bilateral adnexal masses. In the postoperative histopathological evaluation, mixed epithelial carcinoma with areas of disseminated serous adenocarcinoma and less prevalent areas of malignant transitional cell carcinoma was observed. Up-to-date, there have been only two cases with mixed serous adenocarcinoma and malignant transitional cell carcinoma reported in the English literature, and our case is the first case with bilateral tumors.