A 74-year-old man was hospitalized due to hematemesis. Upper gastrointestinal endoscopy revealed a very large and dark red mass in the cardiac region of the stomach that extended from the upper esophagus. A biopsy specimen showed hemorrhagic tissue and no malignant cells. The tumor-like region ulcerated at 5 days after the administration of intravenous lansoprazole at a dose of 30 mg twice a day and resolved with scar formation at 2 months after a change to oral rabeprazole at a dose of 10 mg/day.We diagnosed the patient with gastroesophageal submucosal hematoma. Gastroesophageal submucosal hematoma is a rare complication. In this case, we could follow the process of its disappearance by endoscopy.