Black stools after gastroscopy may be caused by bleeding from damage to the digestive tract that occurred during the gastroscopy. Gastroscopy involves inserting a tube with a mirror of a certain length into the digestive tract of the human body, observing the condition of the mucosal walls in various parts of the digestive tract during the insertion process, and then gradually pulling out the tube. Therefore, the insertion or extraction process is likely to damage the fragile mucosal wall of the GI tract, resulting in bleeding. The production of black stool is often a case of upper gastrointestinal bleeding, the upper and lower gastrointestinal tract is divided by the upper end of the jejunum, and the maximum length of the gastroscope happens to be exactly this position, so the appearance of black stools after gastroscopy is most likely to be caused by the mechanical damage of the examination operation. It may also be the effect of food. If the above situation occurs, please consult a doctor in time for reasonable and standardized diagnosis and treatment.