We report a patient with ulcerative colitis complicated with idiopatic interstitial pneumonia, in whom the etiology of interstitial pneumonia was unknown, but immunological disturbance might have been involved. There are many complications with ulcerative colitis, but interstitial pneumonia is quite rare and its prognosis is quite poor. Antibiotic and steroid treatment were given under respiration supported therapy, but no response could be obtained. In the treatment of patients with ulcerative colitis, we must be mindful of interstitial pneumonia because the prognosis is quite poor.