Abstract: Objective To evaluate the effects of a school-based smoking intervention among adolescents injunior high schools,and to explore the difference in effects of once and multi-inter vention.Methods Twenty-five junior high schools were rando mlyassigned into three groups,which were control group,once-intervention group and three-times inter vention group respectively.All students from the seventh grade of each school were subjects.Every six months after each inter vention there was a questionnaire investigation carried out among the three groups.Results One and half years after intervention,the smoking prevalence of once-intervention group was significantly lower than the control group(OR=0.56,95%CI=0.33~0.87).After the second(OR=0.32,95%CI=0.15~0.63)and third intervention(OR=0.27,95%CI=0.13~0.48).There were fewer smokers in three-times intervention group than the control group.Meanw hile,the smoking prevalence in after the three-time intervention group was found significantly lower than that of once-inter vention group third intervention(OR=0.48,95%CI=0.28~0.81).Conclusion The intervention deliver ed in the study was effective on reducing to-bacco use among students injunior high schools and the effect of three-times intervention on decreasing smoking prevalence was stronger than once-inter vention.