The purpose of this study was to identify the factors that related to obesity among 6th grade elementary school girls. The study subjects were 337 girls residing in Seoul. Not only variables of nutritional environment such as eating habits, health related behavioral variables, nutritional feeding methods during infancy, and genetic factors but also sexual maturity had been included as a obesity related factors. Association between obesity and related variables were analyzed by $x^2$(Chi-square) test. The obesity prevalence of the study subjects were 16% based on Röhrer Index(RI). Fifty-three percent of the study subjects experienced menarche at the time of data collection. Result of analysis showed that not only the nutritional enviromental variables such as eating habits, specific food preferences, and habit of exercise but also genetic factors did not show any statistically significant association with obesity. Above finding may imply that more variables other than the variables included in this study might have influenced on the obesity of the children. However sexual maturity in term of breast development showed significant association with obesity.