We surveyed full‐time employees of ongoing mentoring relationships to investigate relationships among mentors' perceived organizational support (POS), the extent of mentoring functions protégés received, and protégés' POS. Moreover, we examined the moderating role of mentors' altruistic personality in the relationship between mentors' POS and mentoring functions received. Results showed that mentors' POS was positively related to the extent of mentoring protégés reported receiving, which was then related positively to protégés' POS. Furthermore, the extent of mentoring received partially mediated the relationship between mentors' POS and protégés' POS. We also found that mentors' altruistic personality moderated the positive relationship between mentors' POS and the extent of mentoring received such that this relationship was stronger for low altruistic mentors. Theoretical and practical implications of the findings are discussed. Copyright © 2013 John Wiley & Sons, Ltd.