With technological advancements and the increasing nature of complexity and uncertainty in the business world, the development of career adaptation skills is one of the significant factors affecting the success of undergraduates. However, the controversial findings regarding the determinants of career adaptability have triggered this study to question what antecedents would predict undergraduates' career adaptability. Proactive personality on career adaptability in the literature is a hotspot for study in the subject of career adaptability. However, it has been recognized that empirical research on this issue in the context of Sri Lanka is insufficient. Furthermore, the mediating role of this relationship as an intervening mechanism is about to be understood, and there is a knowledge gap in the literature. The major contribution of this research is to expand the knowledge and examine the direct and indirect impact of proactive personality on career adaptability under the mediation role of entrepreneurial self-efficacy. Data is collected using selfadministered questionnaires and distributed using the convenience sample technique among 120 undergraduates studying entrepreneurship degree programs at five state universities in Sri Lanka.The results indicate that a proactive personality significantly and positively impacts career adaptability. Furthermore, the findings revealed that the indirect impact of a proactive personality on career adaptability, mediated through entrepreneurial self-efficacy, was significant. The results of this research assist university mentors, coaches, and policymakers in conceptualizing and implementing relevant interventions and projects that incorporate university support for transitioning undergraduates to a more dynamic work world.