Rectal ulcer with blood in stool is mainly considered to be caused by diseases, such as proctitis, ulcerative colitis, rectal cancer and so on. 1. Proctitis: proctitis is an inflammatory disease that occurs on the surface of rectal mucosa, which is mainly caused by foreign body damage to the intestines, or inflammatory stimulation and other factors. Inflammatory stimulation can cause vasodilatation of rectal ulcers, easy to appear bleeding, erosion of the situation, often manifested as mucus stools, bloody stools, abdominal pain and other symptoms. 2. Ulcerative colitis: ulcerative colitis can involve the rectum, which will lead to rectal ulcers, manifesting as abdominal pain, diarrhea, blood in stool and so on. 3. Rectal cancer: Rectal cancer is a malignant tumor occurring in the epithelial cells of rectal mucosa, which may be asymptomatic in early stage, but due to the enlargement of tumor in later stage, it will compress the local area, resulting in the damage of mucous membrane on the surface of rectal tumor, and necrosis, and then there will be blood in the stool and so on. It is recommended that the patient should seek medical treatment in time, and the doctor should clarify the cause of the disease and then carry out targeted treatment.