Here we report a rare case of inflammatory myofibroblastic tumor of the retroperitoneal space. A 46-year-old woman had had microscopic hematuria for 5 years. Ultrasonographic examination for screening revealed two solid tumors adjacent to the right kidney. These tumors were suspected to be malignant fibrous histiocytoma or liposarcoma by computed tomography and magnetic resonance imaging. She underwent resection of these retroperitoneal tumors and additional right nephrectomy because these tumors were adhered to the kidney and liposarcoma was highly suspected on frozen sections. Histopathologic examination finally revealed that the tumors were inflammatory myofibroblastic tumor arising within Gerota's fasia. She has been followed up for 9 months without any evidence of local recurrence.