A case of ulcerative colitis in which the presence of Listeria monocytogenes was confirmed in the resected colon with polymerase chain reaction and subsequent Southern blot analysis and immunohistochemistry using antibody against Listeria is presented. The patient developed ulcerative colitis at the age of 59 years. Prednisolone, 50 mg/day, was given for severe ulcerative colitis. Later the disease became fulminating, indicating colectomy 4 months after the onset. Multiple sealed colonic perforations were observed. Numerous L. monocytogenes were found at the site of perforation, in fissures, and in cracks in the submucosa. This case indicates the possibility that L. monocytogenes contributes to the exacerbation of colitis to fulminating and colonic perforation.