A patient with malignant pseudomyxoma peritonei underwent a palliative surgical resection and intraperitoneal lavage with 5% dextrose. One hundred and twenty-five mg of cisplatin resolved in 1,500 ml saline was infused into the peritoneal cavity through the reservoir, and the patient was treated with hyperthermia (Thermotron RH 8). As a result the tumor markers (CEA, CA 19-9, and CA-125) markedly decreased after two courses of chemo-hyperthermia. These results suggest that intraperitoneal chemo-hyperthermia is an effective treatment for non-resectable malignant pseudomyxoma peritonei.