The purpose of this study was to examine the mediating role of the career decision level (decidedness and comfort) of South Korean college students regarding the relationships between academic self-efficacy and career preparation behavior. For this purpose, the study collected and analyzed data on 296 South Korean college students using SPSS 22.0 and Hayes’ (2013) Process Macro tool. The results of the study are as follows. Academic self-efficacy was positively associated with career decision level and career preparation behavior, and career decision level was positively associated with career preparation behavior. In terms of the mediation effect, the career decision level partially mediated the relationships between academic self-efficacy and career preparation behavior. The results of the study provide useful suggestions for interventions in the career counseling of college students.