Stool with black residue may be due to dietary factors, medication factors, gastrointestinal bleeding. 1. Dietary factors: consumption of animal blood products such as pig blood, duck blood, etc., due to the food contains hemoglobin, in the gastrointestinal tract in the digestive process will not be partially digested and absorbed, which leads to stool with black residue. 2. Drug factors: when taking drugs containing metal agents such as ferrous sulfate, colloidal bismuth pectin, such drugs in the digestive tract will be partially not be utilized in the gastrointestinal tract and gastric acid and other substances to react and lead to stool with black residue. 3. Digestive tract diseases: when there are digestive tract diseases such as upper gastrointestinal bleeding, ulcers, the blood in the digestive tract through the gastrointestinal tract after digestion, part of the red blood cells that are not digested by the digestive tract through the feces, so there will be a black residue in the feces. If you have black residue in the stool, you should go to the hospital and have a doctor make a treatment plan according to your condition to avoid delay.