A 27-year-old man with fever and dyspnea was admitted to our hospital. Chest computed tomography and a lung biopsy were performed, and bronchiolitis obliterans-organizing pneumonia (BOOP) was diagnosed. The patient was treated with corticosteroid, and a marked improvement was noted. However, when the dosage was tapered, BOOP recurred. Although the dosage was increased again, the corticosteroid alone was no longer effective against BOOP. While continuing with corticosteroid therapy, we also put the patient on a daily regimen of cyclosporin and pirfenidone, a recently developed anti-fibrotic agent. Both drugs were administered orally, and were so effective that we gradually decreased the dosage of corticosteroid. Several journals have reported that cyclosporin may be effective in the treatment of interstitial pneumonitis associated with collagen disease. We concluded that cyclosporin may also be useful in the treatment of refractory BOOP.