Bronchiolitis obliterans organizing pneumonia(BOOP) is a type of diffuse interstitial lung disease that has emerged in the past decade as an important cause of acute respiratory illness in adult. Clinically, the entity usually starts with a subacute influenza-like illness, followed by cough, progressive dyspnea, and weight loss. Organized inflammatory polypoid materials predominantly affecting distal bronchioles, alveolar ducts, and peribronchial alveolar spaces are a key pathologic findings. BOOP is characterized by a good response to glucocorticoid and an excellent prognosis. However, there is a subset of BOOP who presents with a fulminant course leading to death or chronic severe fibrosis with marked impairment of lung function. Recently, we have experienced a case of rapidly progressive BOOP, diagnosed by open lung biopsy and showed a reluctant response to corticosteroid.