Black-green stools may be related to daily diet, but also may be caused by pathological factors such as gastrointestinal bleeding, drug reactions, and so on. 1. Dietary factors: when you have recently taken a lot of vegetables containing chlorophyll such as bok choy and oleaginous vegetables, the chlorophyll in the vegetables will not be fully absorbed in the digestive process of the human body, and thus the stool can be blackish-green in color. Secondly, cuttlefish juice, black fungus, animal offal such as pig liver, foie gras and other food after digestion, the stool will also show a black-green color. 2. Gastrointestinal bleeding: when bleeding is caused by gastric and duodenal lesions, the hemoglobin in the digestive tract of the patient contains a large amount of iron, which will turn into black ferrous sulfide under the action of intestinal bacteria, so the patient’s stool can be black-green. 3. Drug reaction: when the patient is undergoing drug treatment, some drugs will also have an effect on the patient’s stool, such as taking iron, bismuth potassium citrate and other drugs, black stool will also appear. When the patient is not feeling well, he should go to the hospital immediately.