A 19-year-old woman in her 6th month of pregnancy was admitted to our hospital after passing a massive bloody stool. Romanoscopy and upper gastrointestinal panendoscopy revealed no abnormality, but a superior mesenteric arteriography demonstrated an embryonic artery with the extravasation of contrast medium in the distal end of the ileal artery. After the diagnosis of a bleeding Meckel's diverticulum had been established, an emergency operation was successfully performed. At laparotomy, a Meckel's diverticulum was found, about 70 cm toward the oral side from the ileocecal valve, and part of the ileum, including the diverticulum, was resected. Histological examination indicated that the diverticulum had a normal ileal layer with ectopic gastric mucosa and pancreatic tissue. Furthermore, multiple ulcers were observed in the adjacent ileum. Blood coagulation was observed at the site of one of these ulcers, and this was presumed to be the source of the hemorrhage.