We report here an extremely rare case of proliferative Brenner tumor with borderline mucinous cystadenocarcinoma of the ovary, metastasizing to the pleura in a 75-year-old woman. Massive pleural effusion were present due to metastasis and pseudo-Meigs’ syndrome. The cytological findings from pleural effusion, ascites and tumor imprint were similar, suggesting mucus-producing malignant tumors. After receiving a thoracic drainage for pleural effusion, the patient underwent an exploratory laparotomy to remove the left-ovarian tumor. Histopathological examination revealed proliferative Brenner ovarian tumor with borderline mucinous cystadenocarcinoma, and immunohistochemical examinations for the tumors, even mucus-rich tumor cells were positive for CK 7 and negative for CK 20, suggesting the tumor arising from transitional cells, not from mucus-producing ovarian surface epithelial tumor cells. She underwent four courses of chemotherapy with paclitaxel and carboplatin. The patient showed no signs of recurrence 16 months after the surgery.