A 53-year-old male was admitted to our hospital with fever and chest pain. A chest X-ray film showed infiltrative shadows in the right upper and middle lung field. In spite of administration of antibiotics, the chest X-ray film revealed gradually increasing infiltrates and a new shadow appeared in the left upper lung field. The open lung biopsy specimen showed bronchiolitis obliterans organizing pneumonia (BOOP). There was marked roentgenographic improvement in response to steroid therapy. Very few cases of BOOP associated with ulcerative colitis have been reported.