Black stool may be caused by eating animal blood products and other physiological reasons, this situation does not matter; there may be peptic ulcer, peptic tumors and other causes of gastrointestinal bleeding caused by pathological reasons, this situation is recommended to consult a doctor in a timely manner. 1. Physiological causes: intake of pig’s blood, spinach, red amaranth and other foods, due to hemoglobin, phytochrome is not fully metabolized, resulting in black stools and other conditions; taking iron, bismuth and other drugs, such as ferrous sulfate, bismuth pectin, may also cause black stool color and other symptoms, this situation is not a cause for concern, it belongs to the normal situation. 2. Pathological causes: (1) Upper gastrointestinal bleeding: such as bleeding from esophagus, stomach, duodenum, bile duct, pancreatic duct, etc. Common diseases include esophagitis, peptic ulcer, gastric polyp, acute gastric dilatation, gallbladder stones, liver cancer, pancreatic cancer and other diseases, which can cause bleeding, resulting in vomiting of blood, black stool and other symptoms. (2) Lower gastrointestinal bleeding: such as intestinal tuberculosis, intestinal polyps, intussusception, amoebic dysentery, Crohn’s disease, colon polyposis and other diseases, can cause abdominal pain, nausea, diarrhea, black stool and other symptoms. Black stool may also be epidemic hemorrhagic fever, hemophilia and other causes, it is recommended to consult a doctor to clarify the diagnosis, under the guidance of the doctor for targeted treatment.