This disease, also known as nonspecific ulcerative colitis, is an inflammatory process confined to the mucosa and submucosa of the colon. The lesions are mostly located in the sigmoid colon and rectum, but may also extend to the descending colon or even to the entire colon. The pathology is long and often recurrent. The disease is seen at any age, but is most common between the ages of 20 and 30. The disease may be associated with autoimmunity (abnormal immune function such as autoantibodies, immune complexes and abnormal cellular immunity), allergic reactions (individual patients have a history of food allergies, etc.), psychological factors (emotional changes such as anxiety, depression, grief, etc.), environmental and genetic factors and infection (causing vasodilation, increased permeability, intestinal mucosal congestion, edema, erosion and ulceration, etc.). Inflammation is mainly located in the mucosal layer, but can also involve the submucosal layer and rarely reaches the muscular layer, with a uniform and continuous distribution of lesions, during which changes such as edema, congestion, hemorrhage, necrosis and fibrosis of the tissue occur. The disease starts slowly in most cases, with a few acute onset. The course of the disease is mostly long, ranging from several years to more than ten years, often with recurrent attacks or continuous aggravation, and occasionally with an acute fulminant process. Mental stimulation, exertion, and eating disorders are often the triggers for the onset of the disease. It should be differentiated from Crohn’s disease, irritable bowel syndrome, chronic bacterial dysentery, amoebic dysentery, colon cancer, colonic schistosomiasis, ischemic colitis, intestinal tuberculosis, pseudomembranous enteritis, radiation enteritis, colonic polyposis, and colonic diverticulum.