AIMS: Korean National Growth Chart was newly developed at 2007. Prevalence of obesity is expected to be changed according to reference data. This study was performed to compare the prevalence of obesity based on the newly developed growth curve with that of previous data. We also investigate the incidence of obesity, overweight, and normal criteria by two kinds of growth curves. Method: We obtained weight, height from 438 middle school students and 1786 high school students. We divided enrolled students into four groups (middle school boys, middle school girls, high school boys, high school girls). The obese, over weight group was defined as BMI(body mass index) more than 95th, 85th${sim}$94th percentile respectively for age and sex. Obesity by relative weight was defined more than 20% of ideal body weight. We compare the prevalence of obesity in each group by the newly developed Korean National Growth Chart in 2007 and that in 1998. Result: Prevalence of obesity by BMI based on 2007 Korean National Growth Chart and that in 1998 were 8.2-12.9% and 9.0-20.4% respectively. The concordance rate were 99.0%-100% in obese group and 45.0%-91.9% in overweight group according to two kinds of reference data. Prevalence of obesity by relative weight was 11.7-23.0% that was same between 2007 Korean National Growth Chart and that in 1998 except middle school boys group. Conclusion: We found that there is a decrease in prevalence of Obesity by BMI based on 2007 Korean National Growth Chart. It is necessary to evaluate correlation between criteria for obesity and obesity related comorbid conditions for finding proper BMI or relative weight cut off value to prevent obesity and obesity related complications effectively.