Supracondylar nailing is one of the treatment methods for supracondylar fractures of the femur but it needs arthrotomy. We introduce a mew technique of supracondylar nailing under the arthroscopy without arthrotomy. It is closed reduction and intramedullary supracondylar nailing under the arthroscopic control. The potential benefits of this method are decreased unnecessary soft tissue dissection, excellent intraarticular visualization and reduction, decreased blood loss and shortened operative time and postoperative rcovery. We performed this new technique on 4 cases of supracondylar fractures of the femur. Theresults were as follows; 1. Among the 4 cases, 3 cases were AO type A and 1 case was AO type C. 2. All cases showed bony union and average range of knee motion was 110 degrees. 3. The operation time ranged from 60 minutes to 170 minutes and averaging 110 minutes.