Purpose: This article aims to present a unique dimension to mentor studies in that unlike most research that focuses on the novice-teachers-mentee, this study explores the influence of mentoring on the mentors themselves. Two main questions were examined: "Which components of mentoring influence the mentors' professional development?" and "What is the differential impact of each of these components as they are internalized by the mentors?" Design/methodology/approach: A total of 765 mentors completed a questionnaire composed of 47 multiple-choice questions and an open-ended question describing the contribution of mentoring. The survey thus generated both quantitative and qualitative data. Findings: The results show three main components of mentoring that influence mentors' professional development in the following order: personal-emotional, didactic knowledge and systemic-organizational. The findings also illustrate how the mentors used a comparison process to develop their professional perception: first, by comparing their role as a teacher and their role as a mentor, and second, by comparing their own professional identity as a teacher with that of the novice-teacher. Research limitations/implications: The implications of the study point to the importance of mentoring for mentors' professional development. Practical implications of this study encourage mentor training courses that combine a body of knowledge of theory and practice, as well as supervision and mentoring for mentors. It may be important for mentors to develop a professional identity as mentors that is distinct from their professional identity as teachers. Practical implications: The implications of the study point to the importance of mentoring for mentors' professional development. Practical implications of this study encourage mentor training courses that combine a body of knowledge of theory and practice, as well as supervision and mentoring for mentors. It may be important for mentors to develop a professional identity as mentors that is distinct from their professional identity as teachers. Originality/value: The manuscript attempts to explore the dynamic relationships within the mentoring process by investigating how mentoring impacts the development of mentors. It presents insights into the benefits of mentoring novice-teachers for the mentors themselves via analysis of a large-scale, nationwide study.