Intramedullary nailing is one of the most available method in treatment of femoral shaft fracture. Since the development of Kuntscher nail in 1939, new design such as interlocking nail and flexible nail became widely used by more applicable level of femoral shaft fracture. Of complication of IM nailing, matallic failure was rarely seen. The authers clinically analyzed the causes of matallic failures in 10 cases out of 330 cases of intramedullary nailing for treating femoral shaft fractrue. The survey as summerized as follows :1. Metallic failure occured in 5 Kuntscher nail including interlocking nail, 4 Ender nail, 1 PGP nail. 2. Incidence was 2.1% on Kuntscher nail, 5.5% on flexible nail. 3, Metallic failure occured from 1 to 13 months following open reduction and internal fixation. Mean time interval between internal fixation and failure was 7.6 months. 4. The probable causes of metallic failure. 1) Kuntscher nail; Incorrect selection of implants and too early weight bearing may be considered. 2) Interlocking nail; Incorrect position of screw hole corresponding on fracture site and too early weight bearing may be considered. 3) Flexible nail; Inadequate postoperative treatment and loss of medial butress on fracture site may be considered. 5. 7 cases were reoperated with 5 plate fixation, 1 Ender nailing, 1 interlockng nail. 3 cases were managed with conservative treatment. All cases accomplished sucessful bone union.