A 65-year-old man had been hospitalized for examination of melena at a separate facility. Computed tomography (CT) showed left renal mass and he was referred to our hospital. Magnetic resonance imaging (MRI) revealed a tumor without adipose components in the perirenal space. Preoperative diagnosis was retroperitoneal malignant tumor. Tumor excision and left nephrectomy were performed. Pathologic evaluation revealed inflammatory liposarcoma. He has been followed up for 10 months with no additional treatment and no evidence of local recurrence was seen.