Background: Despite recent progress in adjuvant and perioperative chemotherapy, the prognosis of patients with type 4 scirrhous gastric cancer remains poor due to a high risk of peritoneal metastasis. We have previously developed combination chemotherapy regimens of intraperitoneal (IP) paclitaxel (PTX) and systemic chemotherapy, and promising clinical efficacy was reported in gastric cancer with peritoneal metastasis. Herein, a multicenter, open-label, randomized, phase III study is proposed to verify the efficacy of IP PTX to prevent peritoneal recurrence. Methods: Gastric cancer patients with type 4 tumors and without apparent distant metastasis, including peritoneal metastasis, will be randomized for standard systemic chemotherapy or combined IP and systemic chemotherapy based on peritoneal lavage cytology findings. Those with negative peritoneal cytology will receive radical gastrectomy and adjuvant chemotherapy of S-1 plus docetaxel (control arm), or S-1 plus intravenous and IP PTX (experimental arm). Those with positive peritoneal cytology will receive three courses of S-1 plus oxaliplatin (control arm), or S-1 plus oxaliplatin and IP PTX (experimental arm). Subsequently, they undergo gastrectomy and receive postoperative chemotherapy of S-1 plus docetaxel (control arm), or S-1 plus intravenous and IP PTX (experimental arm). The primary endpoint is disease free survival after a 3-year follow-up period. Secondary endpoints are overall survival, survival without peritoneal metastasis, safety, completion rate, curative resection rate, and histological response of preoperative chemotherapy. A total of 300 patients are to be enrolled from 40 hospitals throughout Japan. Clinical trial information: jRCT2031200087.