The gastrointestinal (GI) tract is one of the commonly affected organs in amyloidosis. However, it is difficult to make a correct diagnosis of GI amyloidosis because of its varied clinical manifestation and nonspecific endoscopic findings. Moreover, GI bleeding as a presenting symptom is rare, but can be serious in some cases. Therefore, missed diagnosis and delayed management in GI amyloidosis may potentially lead to a critical outcome. We report a 51-year-old man with multiple myeloma whose major symptom was massive hematochezia due to GI amyloidosis. In our case, amyloid deposits could be distinctly visualized endoscopically in the stomach and the colon. They were manifested as submucosal hematomas in the small bowel resulting in massive bleeding that was successfully controlled with the aid of intraoperative endoscopy.