Understanding what types of social norms are more or less influential and how they operate with respect to other psychological variables can provide valuable insights into the design of effective social norm campaigns. To this end, this study explores the roles of two types of social norms (injunctive norms and descriptive norms) and two types of drinking motives (social motives and conformity motives) in collegiate drinking behavior in South Korea. A survey of Korean college students (N = 569) revealed significant positive effects of injunctive norms, descriptive norms, and social motives on students' drinking frequency and quantity. Conformity motives were positively related to the frequency of drinking but negatively related to the quantity of drinking. Furthermore, the results revealed significant effects of the interactions between descriptive norms and social motives (on both the frequency and quantity of alcohol consumption), such that the positive effect of descriptive norms was more pronounced among individuals with stronger social motives. A similar pattern was observed in the interaction between injunctive norms and conformity motives (on frequency). Theoretical and practical implications of the findings for social norm campaigns seeking to curb drinking among college students are discussed.