Background: Over the last few decades, there have been considerable changes in management of pediatric comminuted long bone fractures (LBF). Flexible intramedullary nails (IMN) were developed to solve the problems of locked IMN in pediatric LBF. Aim: To assess the efficacy of combined external fixation (EF) and flexible IMN (FIN) in unstable LBF in children. Patients and Methods: This retrospective study included 23 pediatric patients with unstable long bone fractures who were treated by combined EF and FIN. Patients were assessed and examined regarding whether or not the fracture had united, leg length discrepancy (LLD), angular deformities and rotational deformities, hip and knee motions, the overall result was evaluated according to Flynn score. Results: All the 11 cases with fractured tibia, had united tibia and 11 out of 12 cases with fractured femur, had united femur. Regarding functional assessment of the studied cases, there were 82.6% have excellent function, 13% satisfactory and only one case (4.3%) poor function. As regards range of motion (ROM); all cases had range of motion grade. Regarding complications, 8.7% had grade I, 4.3% had grade II, and 4.3% had grade III pin tract infection (PTI). There was a significant relationship between age and Flynn criteria. There was ‎ insignificant relationship between fracture type, degree of comminution with functional assessment of studied cases (p=0.270 and 0.228, respectively). Conclusion: Combined use of external fixators and FIN proved to be an effective and reliable approach for managing unstable long bone fractures in children ensuring optimal alignment and stabilization.