Black stools are considered to be related to upper gastrointestinal bleeding as well as the consumption of certain foods and medications. 1. Upper gastrointestinal bleeding: gastric ulcer, duodenal ulcer, stomach tumor, biliary tract tumor, esophagogastric fundus varices and other diseases may lead to upper gastrointestinal bleeding, due to the iron in the blood will be formed in the intestines of iron sulfide, iron sulfide is black, so the stool will be black. 2. Dietary and medication factors: Eating animal blood products or iron supplements may also lead to black stools. Black stools need to go to the hospital, complete the stool routine and other tests, under the guidance of a professional physician to clarify the diagnosis and carry out the appropriate treatment.