Abstract: Objective：Retrospectively analyzed the etiology of lower gastrointestinal bleeding in elderly patients and explored the significance of colonoscopy. Methods：122 cases of elderly patients with acute lower gastrointestinal bleeding were collected from January 2013 to June 2015 in our internal medicine emergency. All the elderly patients were divided into mild bleeding group (59 cases)， moderate bleeding group (52 cases)， and severe bleeding group (11 cases) according to the amount of bleeding and clinical symptoms. All patients underwent colonoscopy to determine the etiology and explore the diagnostic significance of colonoscopy. Results： The three most common causes of the elderly acute lower gastrointestinal bleeding were colon cancer (49 cases， 40.2%)， ischemic enteritis (20 cases， 16.4%) and colon polyps (16 cases， 13.1%). 113 cases of bleeding lesions (92.6%) and 91 cases active bleeding lesions (74.6%) were detected in the study. The detection rate of active bleeding lesions in severe bleeding group was higher than mild and moderate bleeding groups (χ2a=18.516， χ2b=4.153， all P<0.05). Conclusion： The main cause of the elderly patients with acute lower gastrointestinal bleeding in internal medicine emergency were colon cancer， ischemic enteritis and colon polyps. Emergency colonoscopy is of great significance for early diagnosis and treatment of lower gastrointestinal bleeding， especially for moderate and severe bleeding.