A 66 -year-old man presenting with a chief complaint of upper abdominal pain was diagnosed as having an advanced adenocarcinoma, type 2, of the lower third of the stomach after endoscopy was performed. An abdominal computed tomography( CT)scan revealed 4 lymph node metastases at the infrapyloric nodes(station No. 6)and the nodes around the proximal splenic artery(station No. 11p)and the abdominal aorta(station No. 16a2). The clinical stage was determined to be T3(SS)N2M1(LYM), Stage IV. Gastrectomy with D2 plus para-aortic node dissection was scheduled after 2 courses of S-1 plus cisplatin(CDDP)with curative intent. On day 14 after starting S-1 therapy, the patient complained of severe abdominal pain and peritoneal irritation of acute onset. Because the abdominal CT scan showed a large amount of intra-abdominal free air, we performed an urgent laparotomy with a tentative diagnosis of perforation of the gastric cancer. On laparotomy, we found a perforated malignant ulcer, 5 cm in maximum diameter, in the lesser curvature of the stomach; therefore, distal gastrectomy with D1 plus lymphadenectomy and reconstruction using the Roux-en-Y method were performed. At the end of the surgery, a macroscopic residual tumor remained in the para-aortic lymph node. The postoperative course was uneventful, and the patient was discharged on day 23 after surgery. In the present case, despite the performance of urgent gastrectomy while the patient was receiving strong chemotherapy, perioperative management was successful, with no serious postoperative complication or adverse events as a result of the chemotherapy.