We performed combination therapy with modified oxaliplatin/l-LV/5-FU (mFOLFOX) in a patient with recurrent colorectal cancer who had peritonitis carcinomatosis. In this patient, mFOLFOX therapy resulted in disappearance of ascites and a decrease in carbohydrate antigen 19-9 (CA19-9), and improved quality of life (QOL) of the patient. This 62-year-old man was diagnosed with ascending colon cancer and metastatic cancer of the liver. Right hemicolectomy and right hepatic lobectomy were performed. We had started to treat with TS-1 in ambulatory care, however, he had peritonitis carcinomatosis with massive ascite reservoir on CT and peritoneal dissemination after a half year postoperatively. Furthermore, his ECOG Performance Status (PS) was rated as level 3. Therefore, we performed puncture of ascites and palliative mFOLFOX6 therapy. After ten courses, ascites and abdominal induration had disappeared and PS recovered to level 1. At present, CPT-11/l-LV/5-FU (FOLFIRI) are being administered for peripheral neuropathy and metastatic tumor associated with mFOLFOX6. The patient is spending his daily life satisfactory after FOLFIRI without abdominal swelling or ascites, and thus mFOLFOX6 may be an option for palliative therapy against massive ascites in patients with advanced colorectal cancer. The usefulness of palliative mFOLFOX6 therapy for patients with massive ascites should be evaluated in a well-designed clinical trial.Palliat Care Res 2008; 3(2): 316-320