Cytomegalovirus (CMV) infection is common in immunocompetent individuals, causing a mild flu- like illness. Up to 81% of normal healthy individuals aged over 35 have raised CMV antibody titers. However, CMV infection causing colitis is rare but usually fatal. On the contrary, CMV colitis is common in immunosuppressed individuals, especially in those who are Human immunodeficiency virus (HIV) seropositive. We experienced a case of colitis caused by CMV, which was not related with immunosuppression. It remains unclear why the patients developed CMV colitis. Here, we report a case of CMV colitis in an immunocompetent adult, which was confirmed by histopathologic findings through colonoscopic biopsy.