Selective intraarterial administration of CDDP in combination with sodium thiosulfate (STS) was performed in a 39-year-old patient with a malignant ovarian tumor suspected of being a malignant granulosa cell tumor. The primary tumor was in the left ovary, and there were widespread metastases in the abdominal cavity. A total hysterectomy with bilateral adnectomy and partial omentectomy was performed. The tumor showed several different histologic patterns, including serous papillary cyst-adenocarcinoma and granulosa cell tumor of the microfollicular type with Call-Exner bodies in which bizarre nucleoli, deep indentations of the nuclear membrane, nuclear bodies, small mitochondria, lipid droplets, rER, and ribosomes were noted. Serum markers E1, E2, CA-125 and ferritin were elevated. CDDP (total 200 mg) was administered through the abdominal aorta, inferior mesenteric artery, and common hepatic artery in addition to STS, resulting in higher levels of plasma-free platin to the residual tumor. There were hardly any side effects due to this therapy, except for a slight upper digestive tract disturbance and anemia. The result of treatment in this patient was excellent, there is no sign of recurrence, and the serum level of CA-125 3 years after surgery is normal.