The twelve nonunions of distal one-third fracture of femoral shaft after interlocking intramedullary nailing were teated with reaming and exchange nailing with a larger-sized nail, or reaming and exchange nailing with a larger-sized nail added with poller screw fixation. All the femoral nonunion were caused by insecure fixation of the intramedullary nailing, in which a instability of the fracture sites was verified in all cases during operation. The six of them were treated with reaming and exchange nailing. A simultaneous bone graft was performed in one of them to repair the bony defect. The other six of them were treated with reaming and exchange nailing added with poller screw fixation. The result were as follows: l. In six cases that treated with reaming and exchange nailing, patients walked bearing full weight on the extremity with mild aching at the fracture site within 3 months and not obtained a bony union until a 12 months. 2. In one case that treated with reaming and exchange nailing added with poller screw fixation, patient walked bearing full weight on the extremity with mild aching at the fracture site within 3 months and not obtained a bony union until a 12 months. 3. In five cases that treated with reaming and exchange nailing added with poller screw fixation, patient walked bearing full weight on the extremity without aching at the fracture site within 3 months and obtained a bony union within a average of 7 months. From our experience, etiology of nonunions of distal one-third fractures of femoral shaft is thought insecure fixation of the intramedullary nailing due to wide intramedullary canal. We have found reaming and exchange nailing with poller screw fixation is more helpful treatment that reaming exchange nailing as treatment for those fractures.