The primary mediastinal liposarcoma is a very rare tumor. It mainly causes respiratory symptoms, but can be asymptomatic. The most favorable treatment of primary mediastinal liposarcoma is a surgical removal, whether it is complete or not, regardless of the size or histologic type of the tumor. The survival is determined by the histologic type of tumor. A 34-year- ld man was admitted because of asymptomatic mediastinal tumor which was progressively growing over 6 years. The tumor was completely resected and the microscopic findings of the tumor were compatible with well-differentiated liposarcoma. The patient recovered and discharged without complication on the 7th postoperative day.