The present longitudinal study examined the role of quality of friendship in mediating the relation of pro-sociality to self-esteem over time. Participants were 424 Italian young adults (56% females) assessed at two waves (M(age)?=?21.1 at Time 1; M(age)?=?25 at Time 2). An autoregressive cross-lagged panel model was used to test the mediational model. Self- and friend-report measures of pro-sociality, quality of friendship, and self-esteem were included in the analyses. Results were in line with the hypothesized paths, with quality of friendship mediating the relation of pro-sociality to later self-esteem above and beyond its high stability. Self-esteem, in turn, predicted pro-sociality 4 years later. Overall, the present findings support the potential benefits of behaving pro-socially for an actor in terms of increased perceived self-worth and also expand previous work by outlining the specific mediational role of the quality of friendships. The theoretical and practical implications of these results are discussed.