Pulmonary alveolar proteinosis is a rare disease which was described first in 1958 as an ”accumulation of periodic acid-Schiff (PAS)-positive material in the alveolar space”. A 55-year- old male smoker was admitted due to slowly progressive exertional dyspnea with mild productive cough for 9 months. Chest radiography revealed bilateral diffuse lung infiltrates. Arterial blood gas showed hypoxemia with impaired diffusion capacity. Chest tomography showed patchy areas of ground glass opacities with a crazy-paving pattern. Alveolar proteinosis was proved by open- lung biopsy. Therapeutic whole lung lavage was performed 3 times monthly. His symptoms and arterial oxygen tension improved thereafter.