The purpose of this study was to evaluate the effects of smoking prevention programs offered to primary and secondary school students in Seoul, and to analyze factors related to smoking for these students. A quasi-experimental study design was employed and a total of 8,717 students for pre-test and 7,925 students for post-test were participated in the study. The smoking prevention programs included poster and slogan contests. smoking cessation workshop. distribution of smoking prevention pamphlets, reinforcement of smoking regulations, and operation of mobile smoking cessation booth. The results indicated that smoking prevalence decreased after the intervention. However. despite the reinforcement of the regulation related to sales of tobacco to adolescents. more than $50\%$ of the participants still purchased tobacco from stores, while $20.8\%$ obtained tobacco through their friends. Stress, juvenile delinquency, and pocket money were identified as significant factors associated with tobacco use for these students. In conclusion, smoking prevention programs with multiple intervention strategies were effective in decreasing the smoking prevalence among adolescents. Further study is recommended to conduct an experimental study using comparison group to control the effect of other social influences such as national smoking cessation campaigns.