PURPOSE: To compare clinical outcomes and complications between pediatric patients with femoral shaft fracture who had undergone conservative treatment and retrograde flexible intramedullary nailing. MATERIALS AND METHODS: 51 cases of 46 pediatric patients who had femoral shaft fracture were retrospectively studied. Hip spica cast was applied 3~6 weeks after traction in 24 cases of conservative treatment group and closed reduction and internal fixation with flexible nails were performed in 27 cases. RESULT: Neither pain, limitation of joint motion, nor nonunion was reported in both groups. In radiologic evaluation, 4 cases of angulation more than 10 degrees were observed in conservative treatment group and none of surgical treatment group. In leg length discrepancy(LLD) over 10 mm, there was none in surgical treatment group, but 4 cases were seen in the conservative group. Two cases of limping were observed only in the conservative group. Mean time to weight bearing was earlier in surgical treatment group(7.5 weeks) than that in the conservative group(10.8 weeks). CONCLUSION: As treatment of pediatric femoral shaft fracture, retrograde flexible intramedullary nailing had less complications such as LLD and angulation and enabled earlier rehabilitation than conservative treatment.