The purpose of this study was to make a comparative analysis of dietary habits, snacks, eating out and fast-food intake between students with a relatively early sexual maturity and others with a relatively late sexual maturity in a bid to grasp the impact of dietary behaviors on sexual maturity. The subjects in this study were 565 boys and girls who resided in Seoul and Gyeonggi province. They included fifth- and sixth-grade school children and seventh-grade middle school students. To classify the selected students according to the level of sexual maturity, the students of the same month age were divided into two groups in consideration of the stage of their sexual maturity and that of the other age groups. The early mature group was significantly taller and weighed more than the late mature group irrespective of gender. According to Tanner stages, the boys of the early mature group reached a 3.03 stage of sexual maturity when the sexual organs were taken into account, and those of the late mature group reached a 1.50 stage of sexual maturity. The girls of the early mature group reached a 3.43 stage of sexual maturity on the basis of breast, and those of the late mature group reached a 2.73 stage of sexual maturity. Concerning eating out, the early mature group ate out more frequently than the late mature group. In regard to snacks, the early mature group had a snack more often. The findings of the study indicated that there were differences in physical development and some dietary behaviors according to sexual maturity. The early mature group had a snack and ate out relatively more often than the late mature group, which showed that some dietary behaviors had an impact on the sexual maturity of the teens who arrived at the age of puberty.