An 85-year-old female patient presented to the emergency department with the chief complaint of sudden upper abdominal pain. The patient suffered from anorexia and epigastric pain for a month, and a local physician suspected a diagnosis of gastric ulcer. An abdominal computed tomography(CT)scan showed intraperitoneal free air as well as irregular thickening and thinning of the gastric wall. Gastric ulcer perforation was suspected, and an emergency operation was performed. Surgical findings showed thickening of the gastric wall in the pylorus and gastric corpus but partial thinning of areas of the anterior wall of the gastric corpus with a perforation measuring 5 mm. A distal gastrectomy and reconstruction were performed using the Billroth Ⅱ method. The histopathological diagnosis was malignant gastric lymphoma(diffuse large B- cell lymphoma). Considering the patient's age and general condition, chemotherapy was not administered after surgery. The patient was alive without recurrence 8 months after the operation.