Perioperative chemoradiotherapy is considered to be one of the standards of care for early-stage gastric cancer, especially when it involves the esophagogastric junction or greater curvature. To date, there are no reported cases of gastrointestinal perforation in the literature, including many major clinical trials of adjuvant or neoadjuvant chemoradiotherapy for gastric cancer. It is important to recognize and manage this rare, but fatal complication in a timely manner. We report one case of gastrointestinal perforation in a gastric cancer patient undergoing neoadjuvant chemoradiotherapy with 5-fluorouracil and oxaliplatin. A 75-year-old man was diagnosed with stage IV gastric cancer (T4N1M0). We started neoadjuvant chemoradiotherapy with 5-fluorouracil and oxaliplatin. After he finished the first cycle, the patient presented to emergency room with severe abdominal pain of sudden onset. Computed tomography showed moderate pneumoperitoneum and perihepatic fluid. The patient expired 6 hours after he presented to emergency room.