Objective：To investigate the relationship of involvement area with the clinical,endoscopic and pathological characteristics of ulcerative colitis (UC). Methods: We retrospectively studied the clinical,endoscopic and pathological data of 75 patients with UC,including 17(22.67%) with distal colitis,27(36%) with left-sided colitis and 31(41.33%) with extensive colitis/pancolitis. Results: No differences were found in the gender and age of onset between different groups. The incidences of main clinical manifestations and complications increased with the increase of the UC involvement,with significant difference found in the incidences of anemia,hypoproteinemia and extraintestinal manifestations between different groups (P<0.05). Positive correlation was found between the UC involvement with the UC severity (r=0.418,P<0.001) and disease activity under endoscopy (r=0.239,P=0.039). The incidence of atypical hyperplasia of enteric epithelium in extensive colitis/pancolitis group was significantly higher than those in the other 2 groups (both P<0.05). Conclusion: The UC involvement is related to the clinical,endoscopic and pathological characteristics of UC; the involvement is positively correlated with the clinical severity and disease activity of UC under coloscopy.