Tarry stools are usually black in color. Tarry stools are black in color, hence the name black stools, and are often caused by upper gastrointestinal hemorrhage, such as gastric hemorrhage, ruptured varicose vein bleeding in the fundus of the stomach, and duodenal hemorrhage. As the blood stays in the intestines for a long period of time, the red blood cells therein are destroyed, and the hemoglobin combines with the compounds in the intestines to form ferrous sulphide, which leads to the blackish color of the stools. Tarry stools may also be caused by other diseases, such as aplastic anemia, hemophilia, leukemia and other blood system diseases, which may lead to bleeding in the digestive tract. If you have tarry stools, you should go to the hospital in time, usually need to do routine blood tests or other related tests, clear diagnosis and then cooperate with the doctor to take treatment.