Normal stools are yellowish-brown and well formed. Black stool color can be due to certain physiological and pathological reasons, which need to be confirmed by the appropriate examination. 1. Physiological causes: such as taking iron containing drugs, such as ferrous succinate, ferrous sulfate, etc.. Consumption of foods containing more iron, such as animal liver, animal blood products. Eating foods with high pigment content, such as mulberry, purple cabbage, spinach, etc. All of the above can lead to darker stool color. Generally, it will return to normal within 1~2 days after stopping taking it, so there is no need to worry too much. 2. Pathological causes: the pathological cause of black stool is gastrointestinal bleeding, such as gastric or duodenal ulcer, esophageal or gastric mucosal bleeding, gastrointestinal tract tumors, ulcerative colitis, etc., the patient can have black stool. If there is an unexplained black color of stool or a longer duration, it is best to go to the regular hospital for relevant examinations to clarify the cause. When the test results indicate abnormalities, it is necessary to find a specialist as soon as possible for diagnosis and treatment to avoid delaying the condition.