The causes of diarrhea with unformed brown/black stools include physiological causes (including consumption of blood and animal offal, etc.) and pathological causes, mainly upper gastrointestinal bleeding (peptic ulcer, esophageal varices and gastric cancer, etc.), and cancer can not be ruled out as a cause of diarrhea. 1. Physiological diarrhea with unformed brown stools: diarrhea with brown stools may occur when excessive consumption of iron, duck blood, pig’s blood and animal offal occurs, with no other accompanying symptoms or mild symptoms, and the symptoms will disappear after defecation. 2. Pathological diarrhea with unformed brown stool: (1) peptic ulcer: the most common cause, gastric and duodenal mucous membrane damage, up to the mucous membrane muscle layer, the ulcer is too deep and too big caused by bleeding, will appear brown stools, some patients will be accompanied by diarrhea. It is recommended to take omeprazole and other drugs under the guidance of the doctor to relieve. (2) Esophageal varices: In patients with severe liver diseases such as cirrhosis or liver cancer, gastroesophageal varices caused by portal hypertension, excessive pressure damages the blood vessels and bleeding occurs, resulting in brown stools. Endoscopic treatment is used to control the rupture and bleeding of varicose vein vessels; transvenous intrahepatic portosystemic shunt is used to relieve portal hypertension. (3) Gastric cancer: cancer promotes the secretion of gastric acid, destroys gastric mucosa and causes bleeding; the bleeding may be caused by the rupture of cancerous tissues; it leads to brown stool. Early stage can be treated by surgery, and advanced gastric cancer patients need radiotherapy to prolong survival time. When the above symptoms appear, it is recommended to go to the hospital for clear diagnosis in time. Drugs should be used under the guidance of professional physicians, and should not be used arbitrarily on one’s own.