A case of malignant mesothelioma of the peritoneum successfully treated with short-term intraperitoneal chemotherapy is reported. A 67-year-old woman underwent laparotomy for ascending colon cancer. During, laparotomy, numerous mucoid nodules were found on the peritoneal surface, even though the colonic tumor did not invade the serosa. Ileocecal resection (D1) with partial omentectomy was performed. Intraperitoneal infusion with cisplatin (200 mg) was started immediately after surgery and additional cisplatin (150 mg) was administered with OK-432 (30KE). The serum level of CA125 rapidly decreased after the chemotherapy, and was normalized 3 months postoperatively. The histological diagnosis of the peritoneal lesions was malignant mesothelioma of the peritoneum (diffuse type). The patient is living without any evidence of recurrence 10 months postoperatively. These results suggest that this short-term chemotherapy is worth trying in cases of malignant mesothelioma of the peritoneum.