A case of mediastinal liposarcoma in a 45-year-old man is reported. The patient was admitted to the hospital complaining of rhinorrhea. A large mass was found in the right thorax by chest X-ray. At thoracotomy, a tumor measuring 11.5 X 9 X 8.5 cm located in the anterior mediastinum with an extension to the pleural cavity formed in right middle and lower lobes was found and removed from the adjacent visceral pleura. The tumor had a fibrous capsule and was multinodular in external appearance. The cut surface was yellowish and gelatinous. The histological diagnosis of myxoid liposarcoma was made according to the subclassification of liposarcoma proposed by Enzinger et al.