Peer mentoring programs frequently are implemented on college campuses to enhance first-year college student retention; however, few studies have examined characteristics of peer mentors that are associated with more supportive mentor-mentee relationships, leaving college personnel with a limited understanding of how to improve these vital programs. Accordingly, in this prospective study, we examined whether mentors' attachment style and self-efficacy to mentor predicted peer mentors' (n = 76) or mentees' (n = 999) ratings of mentor-provided support. Results showed that mentor self-efficacy mediated the relation between an avoidant attachment style and mentor-reported support; that is, peer mentors with a more avoidant attachment style reported lower self-efficacy to mentor and, in turn, endorsed providing lower levels of support for mentees. Mentor-mentee contact, however, was the only predictor of "mentees'" ratings of mentor support. Future research should aim to extend these preliminary findings so as to inform the selection, training, and supervision of peer mentors in college settings, with the ultimate goal of enhancing first-year student retention.