Cytomegalovirus colitis has been reported infrequently in patients with underlying inflammatory bowel disease, and usually in those who are taking corticosteroid drugs. It has been implicated as a possible exacerbating factor of ulcerative colitis. We experienced a case of cytomegalovirus colitis developed in patient with ulcerative colitis during corticosteroid therapy. So we report the case with a brief review of literatures. (Korean J Gastrointest Endosc 17: 557-560, 1997)