Although dermoid cysts of cystic teratomas of the ovary are almost always benign tumors, the rare development of cancer deserves emphasis. All too often the change that suggest this complication are overlooked at the time of operation, and the correct diagnosis is not made until the opportunity for primary treatment has passed. We have recently experienced a case of epidermoid carcinoma, arising from the benign cystic teratoma of the ovary in a 52-year-old Korean woman, which herein reported and the literatures.