Therapeutic agent for inflammatory bowel disease

Disclosed is 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. 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. The compound shows an unexpected effect beyond a mere antidiarrheal effect.