A 70-year-old man was found to have advanced gastric cancer with a deep ulcer and multiple lymph-node metastases. Although the tumor was resectable, we predicted that the patient would have a poor outcome. We therefore administered neoadjuvant chemotherapy with docetaxel, cisplatin, and S-1 to improve the prognosis before curative resection. On day 15 of chemotherapy, sudden abdominal pain occurred, and we performed an emergency surgery for a diagnosis of panperitonitis due to gastric cancer perforation. The defect in the gastric wall was about 2 cm in diameter and was located in the anterior wall of the antrum, consistent with the center of the tumor. The operative findings suggested that the perforation was caused by chemotherapy-induced necrosis of gastric cancer cells. We saved the patient's life, but intensive care with high-dose catecholamine therapy was needed for several days after the surgery. Gastric cancer perforation induced by neoadjuvant chemotherapy appeared to be more severe than perforation caused by other factors. The adverse effects of chemotherapy apparently increased the severity. Our findings suggest that the risk of gastric cancer perforation should be borne in mind when we administer neoadjuvant chemotherapy to patients who have advanced gastric cancer with a deep ulcer.