Gastroduodenal intussusception is an rare condition usually caused by prolapse of a gastric tumor with subsequent invagination of a portion of the stomach wall into the duodenum. Symptoms are protean, but classically patients have presented with episodic epigastric abdominal distress, a history of intermittent vomiting and gastroduodenal bleeding, either as melena, hematochezia, or stools positive for occult blood. Examination generally discloses a fullness or mass in the epigastrium. Its typical radiologic presentation includes luminal narrowing, distally converging gastric folds, infolding and outpouching of the gastric wall, a filling defect, and a coil-spring pattern. A 71-year-old man was admitted for epigastric pain and melena which required blood transfusions. Endoscopy showed an unexplained pulling-down of part of the gastric body and the pylorus couldn't be identified. An upper GI barium examination demonstrated a huge lobulated mass from the distal antrum of stomach to the duodenal cap. On abdominal sonography, double contour of stomach wall was seen at the proximal portion of narrowing stomach. At surgery, a large, intraluminally exophyting gastric mass prolapsed into duodenum was excised and diagnosed as leiomyoma of stomach.