The utilization of elastic stable intramedullary nail (ESIN) in length unstable femoral shaft fractures in children remains controversial, and the results in different studies vary a lot. This study aims to investigate the clinical outcomes of ESINs versus submuscular plate (SMP) in length unstable femoral shaft fractures.Patients aged 5 to 11 years old with length unstable femoral shaft fractures treated at our institute from January 2008 to January 2018 were included and categorized into ESIN and SMP group. The preoperative data and operative variables were collected from the hospital database, and postoperative data including complications were collected at follow-up visits.In all, 77 patients (8.1 ± 1.9 years old, male 45, female 32) in ESIN group and 45 patients (8.0 ± 2.2 years old, male 26, female 19) in SMP group were included in this study. Comparing operative variables, there was significantly less operative time, reduced estimated blood loss (EBL) and shortened hospital stay for ESINs as compared with SMP (P < .001). However, the fluoroscopy frequency was not significantly different between these 2 fixation methods (P = .42). As for elective removal surgery, there was significantly reduced operative time, EBL and shortened hospital stay for ESINs as compared with SMP (P < .001).Both ESIN and SMP are safe and effective choices for length unstable femoral shaft fractures in children aged 5 to 11 years. In ESIN, extra care is required to provide additional immobilization using spica cast or brace. Compared with SMP, ESIN is able to deliver comparable clinical outcomes with less EBL, operative time and shorter hospital stay.