Mature cystic teratoma is a common ovarian lesion, approximately 10-20% of ovarian tumor. However, it can undergo a malignant transformation, but incidence of malignant transformation is very low. Squamous cell carcinoma is the most common type of malignant transformation in the mature cystic teratoma. Preoperative diagnosis of malignant transformation in the mature cystic teratoma is very difficult, because malignant transformed tissues are very small in the mature cystic teratoma components. And so most of the carcinoma arising in mature cystic teratoma were diagnosed after histologic examination. We experienced a case of squamous cell carcinoma arising in the mature cystic teratoma of the ovary and report a case with a brief review of the literatures.