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.本發明係關於一種將5－氯－6－(2－亞胺基吡咯啶－1－基)甲基－2,4(1H,3H)－嘧啶二酮或其藥學上容許之鹽作為有效成分之炎症性腸道疾病治療藥。根據本發明，可提供一種有效且安全之包括潰瘍性結腸炎及克隆氏症之炎症性腸道疾病之治療藥。該化合物對如炎症性腸道疾病的慢性炎症的治療效果與副作用間之平衡，優於胺基水楊酸製劑或皮質類固醇製劑，而僅具有單純之抑制腹瀉作用，此係完全未預想到者。
