Background & Aim: The prevalence of nonalcoholic fatty liver disease (NAFLD) has emerged worldwide in the last decade. The aim of this study is to estimate the prevalence of NAFLD in South Korean adolescents through a noninvasive method. Methods: Data were obtained from 1416 participants aged 10-18 years from the Korea National Health and Nutrition Examination Survey conducted in 2010 and 2015. Systolic blood pressure (SBP), diastolic blood pressure (DBP), height, weight, waist circumference (WC), body mass index (BMI), fasting glucose, total cholesterol, high-density lipoprotein (HDL), aspartate aminotransferase (AST), alanine aminotransferase (ALT), waist to height ratio (WHtR), pediatric NAFLD fibrosis index ( PNFI) were analyzed. NAFLD was defined as overweight (BMI ≥ 85th percentile) plus elevated ALT (＞ 30 U/L for boys; ＞ 19 U/L for girls). For comparison purposes, three more cutoffs of ALT were used to define NAFLD (＞ 40 U/L, ＞ 30 U/L for both genders and ＞ 25.8 U/L for boys, 22.1 U/L for girls). And NAFLD with fibrosis was estimated by PNFI score over 9. Results: SBP, weight, WC, BMI, WHtR, cholesterol were significantly higher in year 2015 compared to year 2010; P 0.05. Prevalence of suspected NAFLD were 4.7% in 2010 and 5.9% in 2015 ( P = 0.36). Using each of the 3 criteria for elevated ALT (＞ 40 U/L, ＞ 30 U/L for both genders and ＞ 25.8 U/L for boys, 22.1 U/L for girls), NAFLD prevalence were 3.0%, 4.1%, 5.5% and 2.9%, 5.0%, 7.1% in 2010 and 2015, respectively ( P = 0.899, 0.469, 0.289). Boys have higher SBP, DBP, height, weight, WC, BMI, WHtR, glucose, cholesterol, ALT and lower HDL than girls ( P 0.05). Estimated prevalence of NALFD boys has not been increased in 5 years, but prevalence of NAFLD girls generally increased ( P = 0.063). When estimating NAFLD was done by various methods, we found that the probability of liver fibrosis by PNFI varies between 21.3% and 24.5% ( P 0.05). Conclusions: Estimated adolescent with NAFLD in South Korea varies with different BMI and ALT criteria, but it has been generally increased for 5 years, especially for girls. Liver fibrosis is estimated in about 1/5 of NAFLD patient, and this represents NAFLD might be major problem in adolescent of South Korea and suggest aggressive method is needed to evaluate NAFLD. And upper normal limit of BMI and ALT should be modified for Korean adolescent NAFLD.