We examined safety and efficacy of hypotonic CDDP intraperitoneal administration followed by systemic chemotherapy using MTX/5-FU and UFT. Between 1998 and 2004, seven patients who had histologically proven gastric adenocarcinoma with peritoneal metastases underwent palliative gastrectomy at Niigata University Medical Hospital. For residual peritoneal tumors, 100 mg/body of CDDP diluted with distilled water was intraperitoneally administered to the patients before closure of abdominal wall and was drained 30 to 60 minutes after administration. During the postoperative period, a patient suffered from intraperitoneal abscess and another patient had a renal dysfunction with an increasing level of serum Cr (2.1 mg/dl). As adverse effects of the following systemic chemotherapy, three patients had grade 3 anemia and one had grade 3 leukopenia. The median time to progression was 109 days and the median survival time was 248 days. Although intraperitoneal CDDP administration is safe to be carried out intraoperatively, the effect on survival is not better than new anticancer drugs, such as TS-1 and paclitaxel.