An infant with refractory pulmonary alveolar proteinosis (PAP) associated with severe interstitial pneumonia is described. Although she was treated by bilateral simultaneous lung lavage utilizing extracorporeal membrane oxygenation and steroid therapy, she died of progressive respiratory failure 28 days after admission. Histologic examination of lung autopsy specimen showed only partial alveolar spaces to be filled with a dense PAS positive granular eosinophilic material and showed severe interstitial pneumonia with marked fibrosis of alveolar walls and interstitium. The lung lavage seemed to be effective for PAP because the effluent fluid sufficiently became clear and the PAS positive material was detected only in partial alveoli. The full venoarterial cardiopulmonary bypass with extracorporeal membrane oxygenation seemed to be very useful to support bilateral lung lavage for small infants. The refractory symptoms and failure of treatment were resulted from the association of severe interstitial pneumonia. In neonates or infants with PAP and severe interstitial pneumonia with poor response for steroid therapy, the lung transplantation should be considered.