Diverticulum of the horizontal portion of the duodenum is a rare cause of upper gastrointestinal (GI) bleeding. Since it is difficult to access the horizontal portion of the duodenum by standard upper GI endoscopy, only a very few cases of endoscopic hemostasis have been reported. Herein, we report a case of diverticular bleeding from the horizontal portion of the duodenum for which hemostasis was achieved using a small-caliber colonoscope, which has an insertion part designed with a passive-bending function/high-force transmission and a transparent tip hood.