A 77-year-old woman visited our hospital with a history of upper abdominal pain. She had undergone extended cholecystectomy for gallbladder cancer 36 months earlier, and 28 months after the operation, a gastric metastasis was found and she was initiated on treatment with S-1. Abdominal computed tomography revealed a perforation in the gastric antrum and continuous escape of free air from the same area. We made the diagnosis of perforating peritonitis and performed emergency laparotomy. Because there was a large perforation in the anterior wall of the gastric antrum, we performed distal gastrectomy and B-Ⅱ reconstruction. The postoperative course was uneventful and the patient was discharged on the 17th day. We report a case of gastric metastasis from gallbladder cancer complicated by perforating peritonitis.