The purpose of this study was to determine the factors related to eating breakfast for middle and high school students in Seoul using the Theory of Planned Behavior. Out of 2,280 questionnaires distributed to 22 schools, 2,060 were returned (90.4% response rate) and 1,899 were analyzed (83.3% analysis rate). Gender, self-perceived household income level and mother's working status were examined as demographic factors. "Attitude", "Subjective norm", "Perceived difficulty in access to breakfast", "Perceived time restriction" and "Self restriction to breakfast" were extracted as psychosocial factors as the results of factor analysis and reliability test using 17 items. In case of middle school students, boys were more likely to skip breakfast than girls. The students perceiving their household income level "low or middle low" were more likely to skip breakfast than those who perceived their household income level "high or middle high". The students whose mother had a job tended to skip breakfast than those whose mother had no job. In case of high school students, the students perceiving their household income level "low or middle low" tended to skip breakfast than those perceiving their household income level "high or middle high". The results of analysis of variance, all the psychosocial factors examined in this study-"Attitude", "Subjective norm", "Perceived difficulty in access to breakfast", "Perceived time restriction" and "Self restriction to breakfast"- were related to the frequencies of eating breakfast during weekdays in both the middle and high school students.