Objective To summarize the clinical features,management,and outcome of ulcerative colitis (UC) complicated with opportunistic infections in the elderly patients. Methods The clinical data of 43 elderly UC patients in Peking Union Medical College Hospital from 2006 to 2016 were retrospectively analyzed. These patients were divided into two groups for comparisons:the infection group (complicated with opportunistic infection,n=14) and control group (without opportunistic infection,n=29). Results In the infection group,there were 10 men(71.4%),with an average age of (65.0±4.3) years (60-75 years) and a median disease course of 11.0 (3.5,52.5) months. Compared with the control group,the infection group had significantly higher proportion of extensive colitis (78.6% vs. 44.8%,P=0.04). The proportion of severe colitis was also higher in the infection group,but the difference was not statistically significant(50.0% vs. 20.7%;Χ(2)=2.58,P=0.11). Compared with the control group,the infection group had significantly longer hospital stay[(35.7±13.8)d vs.(22.0±15.8)d,P=0.01].The proportions of organ failure and mortality were significantly higher in the infection group[(21.4% vs. 0),(7.1% vs. 0)]. The proportions of emergent operation (50.0% vs. 17.2%;Χ(2)=3.54,P=0.06) and steroid dependence or resistance (64.3% vs. 43.8%;Χ(2)=1.27,P=0.26) were higher in the infection group,but the difference was not statistically significant. Conclusions In the elderly UC patients,opportunistic infection is associated with higher disease activity,higher medical cost,and worse prognosis. Early detection and correct treatment is mandatory to improve patient outcome.