In this study, experimental colitis in rats induced by dextran sulfate sodium (DSS) was performed. Twenty rats freely drank 3% DSS solution for 10 days. During the 10 days, symptoms (diarrhea, hemafecia) were observed daily, and at the same time the rats were colon-endoscopied. After that these rats were killed and their cola taken out to be examined grossly and histologically. It was found that colitis induced by DSS was similar to human ulcerative colitis in symptoms and in pathological changes.