The relationship of obesity and related behaviors was analyzed among 361 primary school children, 4th and 5th grade, in one of private school in Seoul in July 1994. Compared to 1985 Korean Children's Growth Standard, the surveyed children have shown remarkable growth, which is the secular trend in growth of Korean children accompanied with rapid economic growth. But the relative incremental weight was far larger than that of height and this trend was more evident among children over 50th percentile, which shows a wide prevalence of obesity of the surveyed children. By WLI index, 15% of the children was overweight and 13% was obese. The higher the WLI, the more frequent and stronger stress they had. The nutrition knowledge score of obese children was higher compared to others. They were especially sensitive to their physical fitness but many normal or underweight-children also experienced stress due to their body weight and have tried to lose weight by incorrect methods. On the other hand many obese children thought they were optimal or underweight. These results reasserts the importance of nutrition education focused on children aheading puberty. They need to know the correct degree of obesity and to get appropriate education through teachers, dietitians, parents and doctors. The findings of this study could be applied to a nutrition implementation policy to ensure better physical fitness of children aheading puberty in the future.