This study examines the role of dysfunctional career thoughts between two-wave longitudinal data (Time 1 and Time 2) in career decision-making self-efficacy during school-to-work transition periods. Career decision-making self-efficacy was measured before (Time 1) and after college graduation (Time 2). The results indicated that the growth of dysfunctional career thoughts during school-to-work transition periods negatively mediated the two time points (Time 1 and Time 2) of career decision-making self-efficacy. This study also examines the moderation effect of planned happenstance career skills, which refers the individuals’ skills in generating learning experiences during unexpected events on the relationship between dysfunctional career thoughts and career decision-making self-efficacy. College students’ career decision self-efficacy (Time 1) appeared to weaken individual’s career decision self-efficacy after college graduation (Time 2) via dysfunctional career thoughts when students were less likely to have developed planned happenstance career skills in order to discover unexpected career opportunities during school-to-work transition periods.