We report a patient with type 3 gastric cancer with peritoneal dissemination and hydronephrosis who was successfully treated with intraperitoneal infusion of paclitaxel and oral administration of S-1. He was diagnosed with unresectable gastric cancer with severe peritoneal dissemination by staging laparoscopy. We selected combined chemotherapy with both paclitaxel and S-1. Paclitaxel at 60 mg/m(2) was administered intraperitoneally on days 1 and 8, and S-1 at 100 mg/body was administered orally for 14 days, followed by 7 days' rest, as one course. After five courses, primary tumor reduction was confirmed and no cancer cells were detected on pathocytological investigation at second-look laparoscopy. The patient underwent total gastrectomy with lymph node dissection. He died from liver metastasis 29 months after the initial treatment, but he had not suffered from peritoneal metastases and had kept a good quality of life (QOL) since that treatment. This chemotherapy can be applied as one of the promising candidates for the treatment of patients with peritoneal metastasis of gastric cancer.