Dark stools are not necessarily a sign of stomach cancer, but may be caused by digestive disorders or diet, and further gastroscopy is needed to make a definitive diagnosis. Black stool is one of the most common digestive symptoms, which means there is moderate amount of gastrointestinal bleeding. In middle and advanced gastric cancer, black stools appear due to gastrointestinal bleeding caused by tumor erosion of blood vessels, and even vomiting of blood in case of large amount of bleeding. Digestive tract diseases such as acute gastric ulcer, gastric mucous membrane damage, digestive tract blood circulation obstacle appearing digestive tract bleeding, the red blood cells in the blood are destroyed, the hemoglobin in the red blood cells is rich in iron and the sulfide in the intestines to form iron sulfide and lead to black stools. It is also accompanied by stomach discomfort and pain. Diet, such as eating duck blood, pig’s blood, spinach and other iron-rich foods will appear black stools, due to the combination of iron and hydrogen sulfide in the intestinal tract and caused by a physiological phenomenon, there will be no other discomforts, usually 3-5 days after the complete disappearance. If the black stools can not be relieved, and accompanied by other symptoms, it is recommended to further improve the gastroscopy, after a clear diagnosis and treatment.