The authors used 70% deacetylated chitin and cisplatin (CDDP) to devise a novel anticancer drug delivery system (DDS). We examined in vitro release of the CDDP from the system. The novel system was intraperitoneally( ip) given to malignant ascites-bearing mice, and the survival time of each animal was recorded. The related oncolytic mechanism was immunologically investigated. More than 70-90% of the CDDP was gradually delivered from the system in 24 hours. Nineteen animals among 30 treated with our system survived for longer than 4 weeks, and a recurrence of ascites was nil. A 4- week survival rate of the animals with ip injected conventional CDDP was 5/14. All non-treated animals had massive ascites and died within 4 weeks. Immunologic studies suggested that cytotoxic immunoresponse was induced in the mice treated with the novel system. Our newly devised system warrants for clinical applications in the treatment of malignant ascites.