Objective To study the etiolgy and clinical features of pathological fracture in femur. Methods 17 cases of pathological fracture in femur,including 10 males and 7 females with average age 39.5(13～74),were all treated surgically and their pathological diagnosis were achieved,which were consistent with the clinical diagnosis.Results 12 patients (70.59%) suffered from fracture resulted from malignant tumor,of which lung cancer and breast cancer were the commonest with 3 cases respectively (50%).The fracture of proximal end accounted for 65%.8 cases of spontaneous fracture and 2 cases of multiple fracture were all malignancy sufferers.Conclusion Malignancy is the main cause of pathological fracture in femur,of which lung cancer and breast cancer are the commonest.Proximal end of femur is the most frequent part to which fracture happens.Both spontaneous and multiple fractures are resulted from malignancy.