It is not normal for patients to have black stools for three days after gastroscopy, usually normal gastroscopy does not cause gastrointestinal bleeding, so there will be no black stools. Gastroscopy is a common medical examination method, gastroscopy is mainly with the help of a slim, soft tube into the stomach, so doctors can directly observe the esophagus, stomach and duodenum through the gastroscope lesions, especially some relatively small lesions. Under normal circumstances, gastroscopy will not cause gastrointestinal bleeding, so there will be no black stool. After gastroscopy, patients may have black stools for three days because they have eaten animal blood or dark-colored vegetables, or there may be gastric mucosal lesions causing gastrointestinal bleeding. Generally speaking, if the biopsy stimulates the gastric mucosa during gastroscopy, black stools may occur, but most of the black stools will return to normal color after a black stool. It is recommended that patients seek medical examination in time, actively cooperate with the doctor’s treatment, pay attention to bed rest, try to light, easy to digest food, avoid eating too hard, spicy and irritating food.