A 48-year-old woman was referred to our hospital with a 4-year history of chronic diarrhea, for investigation of an abnormal chest radiograph. She was free of respiratory symptoms. Ulcerative colitis was diagnosed by colonoscopic and radiological examinations. A chest radiograph showed a patchy area of consolidation in the right middle lung field and a high-resolution CT showed patchy ground-glass opacities mainly in the peripheral regions. Bronchoalveolar lavage revealed increased percentages of lymphocytes and eosinophils. Thoracoscopic lung biopsy specimens showed the pattern of bronchiolitis obliterans organizing pneumonia, subpleural fibrosis, and interlobular septal thickening. The patient was treated with salazosulfapyridine, 4 g/day, resulting in improvement in her diarrhea, erythrocyte sedimentation rate, KL-6, and the carbon monoxide diffusing capacity of the lungs within 6 months. This is a rare case of ulcerative colitis and associated pulmonary involvement successfully treated with salazosulfapyridine.