Gastrointestinal bleeding from small bowel lesions is uncommon but it is the most common cause of obscure gastrointestinal bleeding that can go undiagnosed using traditional upper endoscopy and colonoscopy. Recently, various new methods, including wireless capsule endoscopy and double-balloon enteroscopy have been used to detect and manage small bowel lesions. A 51-year-old man was admitted with hematochezia. The source of bleeding could not be identified using conventional upper endoscopy and colonoscopy. Wireless capsule endoscopy revealed a mass-like lesion with active blood spurting in the proximal jejunum. Finally, a tumor with central ulceration was detected at the proximal jejunum using a clean colonoscope through the oral approach. This lesion was surgically resected, and the histology findings were consistent with a gastrointestinal stromal tumor. We report a case of gastrointestinal bleeding from a proximal jejunal GIST diagnosed by clean colonoscopy through the oral approach with a review of the relevant literature. (Korean J Gastrointest Endosc 2007;34:219-222)