Diarrhea with blood in stool may be due to ulcerative colitis, bacillary dysentery, colorectal cancer and other diseases. 1. Ulcerative colitis: ulcerative colitis is a kind of inflammatory bowel disease associated with autoimmunity, diffuse inflammation of the colon, can be seen congestion, edema, ulceration, bleeding, often manifested as diarrhea, mucus, pus and blood stools, abdominal pain, and urgency and heaviness (lower abdomen is uncomfortable, very much want to defecate, there is a sense of incomplete defecation after stools) and so on. 2. Bacterial dysentery: Bacterial dysentery is an intestinal infection caused by Shigella dysenteriae, manifested as intestinal mucosal congestion, edema, exudation, common clinical manifestations are abdominal pain, diarrhea, mucus, pus and blood stools. 3. Colorectal cancer: Colorectal cancer is a malignant tumor of colon or rectum, which can be manifested as diarrhea, blood in stools, change of stools’ character and so on. Patients with diarrhea and blood in stool should go to the hospital in time, complete the examination to clarify the cause, and treat according to the cause under the doctor’s guidance.