We report on the rare and surgical treatment of a case of primary mediastinal liposarcoma. A 64-year-old male complained of hoarseness for one month and was admitted to our hospital because of an abnormal shadow, which was postulated to be an anterior mediastinal tumor on a chest computed tomography (CT) scan. Horizontal T1-weighted magnetic resonance imaging (MRI) showed an anterior mediastinal round mass with a signal intensity similar to that of subcutaneous fat, which was 6.5 cm in diameter. An operation similar to extended thymectomy was perfomed through a median sternotomy. Histological examination of the resected specimen revealed that the tumor was composed of well-differentiated liposarcoma and pleomorphic malignant fibrous histiocytoma and the tumor was diagnosed as a de-differentiated liposarcoma. We discuss it with reference to a collective review of the Japanese literature for surgical cases of primary liposarcoma of the mediastinum.