Congenital cystic adenomatoid malformation[CCAM of the lung is extremely rare. We have experienced an unusual case of congenital cystic adenomatoid malformation. The patient was 20-year-old male and had chest pain for 10 days. On simple chest x-ray and Thoracic CT scan, there was a large cystic mass surrounded with multiloculated round cysts with air fluid level on the right lower lobe of a lung. Right lower lobectomy was performed and the pathologic result was congenital cystic adenomatoid malformation.