Retroperitoneal teratoma was described in a 20-month-old intact female ferret (Mustela putorius furo). Retroperitoneal mass about $8{ imes}5$ cm in size was surgically removed and histopathologic examination was performed. Grossly, on cross section of the mass, the consistency was soft to firm and contained several cystic structures which are filled with dried keratinous material. Histologically, the retroperitoneal mass consisted of embryologically heterogeneous tissues that include skin, bone and cartilage, adipose tissue, respiratory epithelium, and exocrine pancreatic tissue. Based on the characteristic histologic features of the mass, a diagnosis of retroperitoneal teratoma was made. Adrenal gland or ovary was suspected as the origin of the tumor.