Pulmonary sequestration is the part of a spectrum of bronchopulmonary foregut anomalies in which a portion of lung parenchyma does not communicate with the tracheobronchial tree and usually receives its arterial supply from a systemic vessel. The sequestrated portion of the lung is susceptible to infection. The patient with this entity will have a paucity of symptoms and will present himself for treatment because of a persistent pneumonia. The associated aberrant systemic artery makes the preoperative diagnosis of the lesion imperative because of the life-threatening technical hazards posed by this artery. We experienced a case of intralobar pulmonary sequestration. Initially, the diagnosis of sequestration was unsuspected and open thoracotomy was done for management of homogenous cystic mass on left lower lobe, but one anomalous systemic artery from thoracic descending aorta to sequestrated lung was incidentally revealed. Then we underwent lower lobectomy and ligation of anomalous artery.