The present invention relates to a therapeutic agent for inflammatory bowel disease comprising 5-chloro-6-(2-iminopyrrolidin-1-yl)methyl-2,4(1H,3H)-pyrimidinedione or a pharmaceutically acceptable salt thereof as an active ingredient. According to the present invention, an effective and safe therapeutic agent for inflammatory bowel disease including ulcerative colitis and Crohn's disease can be provided. The balance between the therapeutic effect on a chronic inflammation such as inflammatory bowel disease and the adverse side effect of the compound is superior to those of an aminosalicylic acid preparation and a corticosteroid preparation, which cannot be expected at all from a mere anti-diarrheal effect.
