Black stool is mainly due to two reasons, one, physiological reasons, including eating dark-colored food, such as amaranth, red bean porridge, animal blood products, such as pig’s blood, duck’s blood, black stool when eating these foods. Second, gastrointestinal bleeding, caused by the common causes of gastrointestinal bleeding mainly peptic ulcer, including gastric ulcer, duodenal ulcer; the upper gastrointestinal tract of the acute gastric mucosal lesions, gastrointestinal malignant tumors in the emergence of bleeding, may appear in the stool color black. Therefore, we need to distinguish which is the cause of black stool, excluding physiological factors should be carried out in addition to gastroscopy, to determine whether there is organic lesions, if necessary, need to carry out small enteroscopy or capsule endoscopy, to observe the small intestine with or without organic lesions.