Dark greenish black stool may be related to dietary factors, medication factors, or diseases such as upper gastrointestinal bleeding. 1. Dietary factors: such as eating green leafy vegetables, pig’s blood, pig’s liver, duck’s blood and other blood products, can cause dark greenish black stool. 2. Drug factors: such as eating iron, such as ferrous succinate, etc., bismuth, such as colloidal bismuth pectin and other drugs, can also cause dark greenish black stool. 3. Upper gastrointestinal bleeding: such as peptic ulcer, acute gastric mucosal lesions, esophagogastric fundus varices, gastric cancer and other diseases, can cause upper gastrointestinal bleeding, resulting in dark greenish black stool. There are many other causes of dark greenish black stool, which should be taken seriously, and timely consultation should be made to identify the cause of the disease and follow the medical advice for further treatment or therapy.