Background&Aims:Non-alcoholic fatty liver disease (NAFLD) is increasing in obese children, but its prevalence and associated risk factors in the prepubertal period still remain elusive because there are few studies on risk factors in obese children. The aim of this study was to evaluate the prevalence of NAFLD in obese children, and to analyze risk factors for developing NAFLD in obese children, respectively. Methods:A total 181children with obesity (65 boys,116 girls;72 prepuberty, 105 adolescents)were recruited from the Pediatric Obesity Clinic. Anthropometric measurements, blood pressure, body composition measurements based on bioelectrical impedance analysis, and the obesity questionnaires were performed at first visit. Fasting laboratory tests including liver enzymes and abdominal ultrasonography were assessed in all subjects. Results:The prevalence of NAFLD was 45% in the prepubertal obese children and 77% in adolescents. In the prepubertal children, there were significant differences in gender(p=0.004), abdominal circumference(AC)(p=0.003), body fat percentage(p=0.038), serum levels of GGT(p0.001), cholesterol(p=0.018), and fasting insulin(p=0.024) between the non-NAFLD and the NAFLD group. In the puberty, there was significant differences in body mass index z-score(p=0.046), AC(p=0.017), sleep duration(p=0.015), fat mass(p=0.017), media exposure time(p=0.015), levels of GGT(p0.001), triglyceride(p=0.020), and HOMA-IR(p0.001) between the non-NAFLD and the NAFLD group. In prepubertal children with NAFLD, Multivariate logistic regression analysis revealed age and body fat percentage as significant risk factors for developing NAFLD in prepubertal children, whereas sleep duration and BMI z-score in adolescents. Conclusion:NAFLD developed even in prepubertal children as obesity-related complications, although NAFLD was more prevalent in adolescents. BMI and some life style factors were significantly associated with NAFLD in obese adolescents, but not in prepubertal children. Obesity-related metabolic abnormalities and increased body fats were key components reflecting the development of NAFLD in young obese children. Therefore, thorough obesity-oriented approach including anthropometry, body composition measurement, laboratory tests, and liver imaging may be beneficial in prepubertal children with obesity suspected of NAFLD.