A 37-year-old man with no particular medical history presented with abdominal pain and vomiting on the day after overeating. Three days later, he was referred to our hospital because of suspicion of bowel obstruction. Physical examination revealed the remarkably distended abdomen and muscular defense at the upper right quadrant of abdomen. An abdominal CT scan showed significant dilatation from the stomach to the third part of duodenum and duodenal emphysema. Emergency laparotomy was performed with the diagnosis of acute gastric dilatation and duodenal necrosis. At laparotomy, the duodenum showed inflammation, but it was not necrotic. As a necrosis portion 5 cm in diameter was found at the upper body of the stomach, total gastrectomy was performed. The postoperative course was uneventful, and the patient was discharged on postoperative day 17. Superior mesenteric artery syndrome can cause gastric necrosis due to the acute gastric dilatation. As the diagnosis is difficult, we should consider emergency laparotomy or follow up carefully.