Mentorship quality is an important aspect of mentorship effectiveness, yet we know little about its predictors. Using social identity theory, we examined the relationship between mentor alcohol use norms and mentorship quality as perceived by proteges. Our study also considered the mediating role of protege identification with the mentor and the moderating role of protege traditionality. The findings, based on mentor-protege dyadic data collected through a three-wave survey in China, indicate that mentor alcohol use norms are negatively related to mentorship quality, and that this relationship is mediated by protege identification with the mentor. Furthermore, the traditionality of proteges alleviates not only the negative relationship between mentor alcohol use norms and protege identification with the mentor, but also the indirect relationship between mentor alcohol use norms and mentorship quality via protege identification with the mentor. The results underscore the value of focusing on mentor behavioral norms that are not directed toward the protege. We conclude with a discussion of the theoretical and practical implications for mentoring research.