A routine chest radiograph in a 10 months old male infant revealed a giant air filled cystic lesion of the left hemithorax under tension. At thoracotomy, a large left lower lobe intraparenchymal cyst required lobectomy and the pathological finding were consistent with a bronchogenic cyst. This kind of parenchymal bronchogenic cyst is uncommon lesion, and we have performed successful surgical resection. After this lobectomy, this patient was complete recovered and postoperative course was uneventful.