Black-green stools may be caused by dietary factors, taking certain medications, upper gastrointestinal bleeding and other factors. 1. Dietary factors: short-term intake of excessive green leafy vegetables, such as spinach, leeks, chard, etc.; or excessive intake of liver and blood products, such as chicken blood, duck blood, pig’s blood, etc., may lead to black-green stool. It is recommended to change dietary habits and stop intake of the above foods so that the symptoms can disappear. 2. Taking certain drugs: taking iron supplements and bismuth drugs such as ferrous sulfate, colloidal bismuth pectin and bismuth potassium citrate for a short period of time. Iron is oxidized in the intestines, which may lead to black-green stools. Stop taking the above drugs, stools can gradually return to normal. 3. Upper gastrointestinal bleeding: duodenal ulcer, gastric ulcer or gastritis combined with bleeding may produce black stool. It is recommended that the patient go to the gastroenterology department of the hospital in a timely manner to clarify the cause. The black green color of the stool is related to many factors, so we suggest that the patient go to the gastroenterology department of the hospital to get a clear diagnosis and active treatment.