This study was conducted to find the differences in the physical changes, eating habits and dietary intake by obseity index of sixth grade primary school students is Seoul.The subjests were classified into three groups, an underweight group(90% under, 12l Ug), normal group(between 90-110%, 153, NG), and obese group(110% over, 91, OG) according to WLI(Weight-Length Index)calculated with their present (6th grade) height and weight. The physical growth of the subjects was generally good, although problems of both underweight and obesity were existed together. The mean heigh growth velocity per year, weight growth velocity per year and WLI changes per year of OG were higher than those of the other groups(p〈0.01). The past physical status of the three groups were maintained from 1 st grade to sixth grade, As eating habits and lifestyles, they were not statistically significant but there were some differences among the three groups. More students of the UG disliked a certain food than those of the other groups. UG liked fried or roasted foods more(p〈0.001). NG tended to eat three meals more irregularly. OG tended to have meal times more regularly and do more regular exercise than the other groups. The dietary intakes of three groups were generally good. They were not statically significant among the three groups. With theses difference among the three groups, it is recommended to educate about unbalanced diet for the underweight group, regularity, of meals for the normal group, doing exercise for the obese for the obese group, and increasing Ca and vitamin A intake for most students, As the physical status for th lower grades have been maintained up to the sixth grade, nutrition education programs should be started at the lower grades in the elementary school.