The causes of black stools are simply divided into two major parts: 1. related to diet and intake of drugs; 2. related to disease. Part of the diet can lead to black stool such as animal offal, and an overdose of particularly green vegetables, such as spinach, green vegetables, and a large amount of meat, such as a large amount of beef and other such foods, as well as the visceral blood of animals, they can lead to the appearance of the color of the stool black; there are also some drugs bismuth preparations and iron preparations, can also make the color of the stool black. 3, due to some diseases of the digestive tract, due to bleeding in the digestive tract, including Esophagus, stomach, duodenum, small intestine, upper colon, etc. If bleeding, as long as the amount of bleeding in more than 5mL can appear positive stool test occult blood, when the amount of bleeding in more than 50mL can appear to be black stool. If the bleeding is in the lower part of the colon, it may be bright red in color, such as rectal and sigmoid colon bleeding, which may be bright red in color. In addition, bleeding in the upper part of the colon and other GI tracts can be black. Therefore, once you notice a black stool, it is important to go to the hospital to look for possible diseases on the one hand, and to see if the patient is taking a diet or medication that causes black stools on the other.