First of all, we should exclude physiological factors, such as consuming food that can make the color of stool become black, etc. Pathological is bleeding in the digestive tract, which is mostly seen in blood diseases, tumors, vascular diseases, ulcerative diseases and so on. 1. Blood disease: for example, thrombocytopenia, leukemia, hemophilia, etc. can appear black stool. 2. Tumors: for example, stomach tumors, esophageal tumors, tumor rupture, bleeding ulcers can cause black stools. 3. Vascular diseases: for example, varicose veins in the esophagus and fundus of the stomach, epidemic hemorrhagic fever and so on, black stools can occur. 4. Ulcerative diseases: for example, gastric ulcer, duodenal ulcer, stress ulcer. Peptic ulcers are a common cause of black stools. If you have black stools, you may have eaten certain foods that have coloring or can darken the color of your stools. If you have black stools, you should consult a doctor to find out the cause of the black stools and to standardize the treatment, so as not to delay your condition.