Korean government enforced a law for the graphic warning labels required to be added on cigarette packages in late December 2016. We take this opportunity to initiate a longitudinal study of the impact of cigarette graphic health warnings on Korean smokers’ cessation behavior. Extant literature investigated incumbent effects of the policy in numerous foreign countries but longitudinal studies investigating changes before and after the newly initiated policy were rarely found. In addition, most of research done in the laboratory reported confounding results supporting both of positive as well as negative effects of graphic health warnings. Based on extended parallel process model(Witte, 1992), a new moderated mediation research framework has been suggested and tested in order to fill this research gap. The results found that graphic health warnings increase smokers’ perceived threat, and their perceived threat would lead to cessation behavior. Yet this mediating effect if perceived threat was moderated by smokers’ self-efficacy. In other words, smokers with low self-efficacy would cease smoking due to high threat but smokers with high self-efficacy would not. Finally, theoretical as well as managerial contributions regards public health policy were discussed.