Liposarcomas are uncommon tumors originated from the primitive mesenchymal cells. Mediastinal liposarcoma is a very rare localization, accounting less than 1% of all the mediastinal tumors. These tumors may remain asymptomatic until they reach a giant size due to pleural space and elasticity of the lungs. Complete resection is not always possible in the poorly differential types invading the mediastinal vital organs. In this article, we presented a 34 years-old man patient with an anterior mediastinum localized liposarcoma that was asymptomatic until last 3 months and reached to giant sizes and complete successful surgical intervention.