Gonadoblastoma is an uncommon ovarian tumor arising primarily in females with gonadal dysgenesis and a 46, XY karyotype. Germ cell tumors arising within and/or overgrowing a gonadoblastoma have been reported. We report a rare case of a malignant mixed germ cell tumor (yolk sac tumor and choriocarcinoma) arising in a gonadoblastoma of the left ovary in a 19-year-old female with a 46, XX karyotype. The patient’s initial α-fetoprotein level was 20 000 KIU/L. The patient underwent a laparoscopic unilateral salpingo-oophorectomy with omentectomy and peritoneal washing followed by adjuvant chemotherapy.