The purpose of the present study was to evaluate cytotoxic agents active for mucinous adenocarcinoma of the ovary (MACO) which is considered to be intrinsically platinum-resistant. We first conducted in vitro chemosensitivity tests assessing cytotoxic activities of various anti-cancer agents against MACO using a cell line, designated OMC-3, established from ascites of a patient with histologically pure MACO. The most active single agent was SN-38 (active substance of CPT-11 in vivo). The second most potent agent was mitomycin-C (MMC) followed by doxorubicin (DOX). In vivo chemo-sensitivity test of agents on OMC-3 transplanted into Balb/c nude mice demonstrated that MMC was most potent, followed by DOX. Moreover, a combination of CPT-11 and MMC exhibited the highest anti-tumor activity in this animal model. Cisplatin was found to be ineffective in both the in vitro and in vivo experimental system. Clinical trial with a combination of MMC and CPT-11 are justified in patients with MACO.