Objective : To get a better understanding of obesity and etiological factors of obesity among school children. Methods : We have conducted a questionnaire survey of 4542 (2395male and 2147female) age from 7-15 in Shanghai School District to study their 24h nutrition intakes ; we have asked all our survey participating students to take a physical exam and body mass index measurement to determine the morbidity of obesity. Common statistic method was used in analyzing the data. Results : The result shows an over all morbidity (boys and girls) of $12.3\%$ among the students we have studied. Our research shows that boys have a higher rate of morbidity of obesity $17.1\%$ vs. $7.0\%$ for girls. The morbidity for boys starts under age 10, reaches the peak at age 10 ($24.3\%$), then declines after age 11 ; as for girls the morbidity starts at under age 9, reaches the peak at 9, and then declines after 10. Our study also indicates that the daily nutrition intake of protein, fat and carbohydrate by the students have satisfied Chinese Dietary Reference Intakes (DRIs), while the daily intakes of calcium, iron, zinc, and vitamin C are below the $80\%$ of the DRIs suggested value. For students who are obese, our study shows that their average daily intakes of calories and protein have reached $90\%$ of the suggested value by the RNI while the intakes of calcium, iron, and zinc are far below standards. Furthermore, our research shows that the obese students usually intake more calories, proteins and vitamin $B_1$, but less for iron and calcium compared to the normal students. Some other factors such as the education and occupation of the parents, especially the mother, the family history of obesity and the eating habits are important factors that should be closely watched. Conclusion : The morbidity of obesity among boys is higher than girls. Obesity is closely related to the family history, the diet habits and the life styles.