Mature cystic teratoma is the most common ovarian tumor, but its malignant transformation is rare and has always been found to occur in the postmenopausal woman. Herein, we report a case of International Federation of Gynecology and Obstetrics (FIGO) stage IIIc squamous cell carcinoma arising from a mature cystic teratoma of the right ovary in a woman of reproductive age. The patient underwent abdominal total hysterectomy, bilateral salpingoophorectomy, omentectomy, and received one course of postoperative chemotherapy. She passed away 9 months after surgery. Related literature is reviewed.