The black substance in feces is usually caused by physiological factors or pathological factors such as bleeding peptic ulcer, inflammatory bowel disease, digestive tract tumor and so on. 1. Physiological factors: may be due to food factors, such as consumption of animal blood products or iron content of spinach and other foods, after digestion can lead to the phenomenon of fecal black material, this situation is normal, do not need to worry too much. 2. Peptic ulcer: If you suffer from peptic ulcer, it will lead to damage to the mucous membrane of the stomach and bleeding, and the blood will react with gastric acid and pepsin inside the gastrointestinal tract, which will be converted to divalent iron ions and excreted with the feces, and then oxidized and transformed into black feces, which will lead to the phenomenon of feces with black substances. 3. Inflammatory bowel disease: in the acute stage, there may be diarrhea, abdominal pain, fever, but also because of inflammation damage leading to intestinal bleeding, also due to gastrointestinal bleeding manifested in the feces of the black material. If accompanied by hemorrhage, urgent medical treatment is needed, and if necessary, surgical treatment. 4. Tumor of digestive tract: patients with tumor of digestive tract may cause tumor rupture in the late stage, and the blood in the stomach reacts with gastric and intestinal fluids, and the blood will turn black, and then form the phenomenon of black material in feces after discharging with feces. If the phenomenon of black substance in feces occurs, it is recommended to observe on your own, if there is no relief, it is recommended to go to the hospital for examination and treatment in time.