A 51-year-old male was admitted due to mediastinal mass. Chest PA showed a $4{ imes}5$ cm sized round mass on right lower paratracheal area. The chest computerized tomogram showed cystic mass located between superior vena cava and trachea. This cystic mass was composed of variable internal architecture with Hounsfield unit(HU) from -44.4 to +25.5. The resected cystic mass revealed ectodermal, mesodermal, and endodermal structures. We report a case of anterior mediastinal cystic teratoma confirmed by open thoracotomy.