Diarrhea with black loose stools may be caused by dietary factors, medication factors, upper gastrointestinal bleeding and other reasons. 1. Dietary factors: Eating a lot of black food, such as black sesame seeds, black beans or eating animal blood products, such as chicken blood, duck blood, etc., may lead to diarrhea black loose stools. 2. Drug factors: taking iron, such as ferrous gluconate, polysaccharide iron complex, and stomach upset taking gastric mucosal protectants, such as bismuth aluminum complex, colloidal bismuth pectin, etc. will cause black loose stools. 3. Upper gastrointestinal bleeding: for example, bleeding from peptic ulcer, rupture and bleeding from varicose veins in the fundus of the stomach due to liver cirrhosis, esophageal cancer, gastric cancer, etc. When the bleeding is not too much, sulfide will be formed in the intestinal tract through oxidation and so black loose stools will be discharged. It is recommended to consult a doctor in time to find out the cause of the disease and then treat it, and do not take medicines by yourself to avoid delaying the condition.