This study examined relationships between mentoring functions offered and transformational leadership as a mentor outcome and affective well-being and organizational commitment as mutual outcomes for both mentors and protégés. For this examination, we conducted a longitudinal field study by using 111 matched reports from both mentors and protégés collected at three different points in time over seven months in nine Korean companies that administered a standardized formal mentoring program. Study results showed that mentoring functions assessed at Time 2 were positively associated with mentors' and protégés' post-mentoring outcomes at Time 3 after controlling for pre-mentoring initial levels of those outcomes at Time 1. Study findings also revealed that relative effects of mentoring on the mentor and protégé outcomes differed by the types of mentoring functions. We discuss the theoretical, practical, and methodological implications from these results. Copyright © 2012 John Wiley & Sons, Ltd.