In this study, we examined the effectiveness of peer support for college women mentors who engaged in one-to-one and group mentoring with at-risk adolescent girls. Using data from 162 mentoring pairs, results suggested that mentor support positively predicted mentees' self-reported improvement after a year of mentoring. An examination of mentees' self-esteem outcomes revealed that mentor peer support was associated with higher outcomes only for those mentees who had higher pre-program scores; for those with below average pre-scores, mentor support was associated with lower self-esteem. Taken together, these results indicate that mentor support may serve as an important function beyond ongoing training, though its effectiveness may vary based on mentee characteristics. Implications are discussed.