A case of dedifferentiated liposarcoma in a fifty-one year old man is presented. The patient received a wide extirpation for a relatively rapidly growing mass in his right gluteal region. The mass was multinodular and consisted of two clearly distinct elements; well differentiated liposarcoma and non-lipogenic spindle cell sarcoma (fibrosarcoma). This is first proven case of dedifferentiated liposarcoma of the soft tissue in Korean literature, and its histogenesis is discussed along the dedifferentiation-redifferentiation pathway of fibrohistiocytic differentiation.