The prevalence of overweight and obesity in elementary school has increased in several surveys. also obesity is increasingly recognised as a health problem by many countries. body mass index is widely used as a measure of ％body at in clinical practice. for adults there are internationally recognised. however, in childhood and adolescence, there has been a lack of agreement about the definition of overweight and obesity. So the purpose is to apply and provide basic data of BMI cutoff points in elementary school and adolescence. the present study evaluated body mass index in 404(3grades; aged 10years) and 392(6grades aged 13years)boys and girls attending in 12 elementary schools. the method to evaluate overweight and obesity in elementary boys and girls is body mass index(BMI ; weight in ㎏/㎡). The mean height in 10 years elementary boys and girls were 132.2±5.48㎠, 130.9±5.54㎠, respectively. the mean height in 13 years elementary boys and girls were 149.7±7.34㎠, 149.9± 6.24㎠, respectively. the mean height was significant difference(p＜0.05) between 10 and 13 years school boys and girls. The mean weight in 10 years elementary boys and girls were 32.3±7.15㎏, 30.2±5.68㎏, respectively. The mean weight in 13 years elementary boys and girls were 46.8±11.34㎏, 44.3±9.16㎏, respectively. The mean weight was significant difference(p＜0.05) between 10 and 13 years school boys and girls. as the result of BMI evaluation, the mean BMI in 10 years elementary boys and girls were 18.34±3.21 ㎏/㎡, 17.52±2.55㎏/㎡, respectively. The mean BMl is significantly greater (p＜.05) for 10 years elementary boys than 10 years elementary girls. the mean BM in 13 years elementary boys and girls were 20.69±3.70㎏ /㎡, 19.57±3.21㎏/㎡,respectively. The mean BMI is significantly greater(p＜.05) for 13 years elementary boys than 13 years elementary girls. and the prevalence of obesity when evaluated BM were as follows mild obesity is 6.78％, moderate obesity 12.94％, and severe obesity 6.03％.