Mature cystic teratoma of the ovary, though it contains derivatives of all three embryonic germ cell layers, rarely presents together with ovarian epithelial or sex cord-stromal tumors. Only a few cases of ovarian cystic teratoma in association with granulosa cell tumor have been reported in the literature, and simultaneous occurrence of mucinous cystadenoma and granulosa cell tumor is even rarer. To our knowledge, there has never been a report of mature cystic teratoma of ovary coexisting with granulosa cell tumor and mucinous cystadenoma. We report a case of mature cystic teratoma, mucinous cystadenoma, and granulosa cell tumor in the ovary of a 40-year-old woman. The involved ovary, massively enlarged by a multiloculated cyst, showed a hair-sprouting mass with a yellow-tan nodule embedded in the cyst wall. Microscopically, three tumor types were revealed: mature cystic teratoma, mucinous cystadenoma, and granulosa cell tumor.