The composite substance of Mitomycin C (MMC) and polymer by low temperature radiating polymerization has a characteristic of slow release, the possibility of applying it to local chemotherapy was clinically studied. Buttom-formed preparation (MMC 20 mg) and needle-formed preparation (MMC 5 mg) were applied to the lesions, respectively, by sewing and piercing in 220 cancer patients with non resectable infiltrative lesions. The treatment had a pain-relieving effect in 70 out of 117 cases (60.0%) of painful cancer in the pancreas, biliary duct, liver, etc, and improved the symptoms of digestive organs in 31 out of 93 cases (33.3%). However, the tumor-reducing effect was recognized only in minute localized lesions of hepatic cancer, etc., and the survival period was not prolonged. The treatment caused no severe side effects. From the above results, the local chemotherapy with slow-releasing MMC preparation was concluded to be a useful means of palliative therapy in non-resectable, though its formulation may to be further improved.