Pulmonary sequestration is an uncommon congenital pulmonary malformations characterized by presence of nonfunctioning lung tissue which receives its blood supply mostly from the anomalous systemic arteries. We have experienced a 30 year old male patient with a mediastinal mass complaining of intermittent chest pain, and the mass was histologically confirmed as extralobar pulmonary sequestration. The anomalous blood supply origined from the right pulmonary artery but there was no communication with the tracheobronchial tree. He underwent operation through midsternotomy incision for the purpose of concurrent resection of enlarged thymus noted on chest CT.