This study was designed to examine the roles of emotional reactivity, self-regulation, and pubertal timing in prosocial behaviors during adolescence. Participants were 850 sixth graders (50 percent female, mean age = 11.03, standard deviation = .17) who were followed up at the age of 15. In hierarchical regression models, measures of emotional reactivity, self-regulation, pubertal timing, and their interactions were used to predict (concurrently and over time) adolescents' prosocial behaviors in the home and with peers. Overall, the findings provide evidence for pubertal and temperament-based predictors of prosocial behaviors expressed in different contexts. Self-regulation was positively related to both forms of prosocial behavior, concurrently and longitudinally. Emotional reactivity showed moderately consistent effects, showing negative concurrent relations to prosocial behavior with peers and negative longitudinal relations (4 years later) to prosocial behavior at home. Some curvilinear effects of temperament on prosocial behaviors were also found. Effects of pubertal timing were found to interact with gender, such that boys who were early maturers showed the highest levels of prosocial behavior at home concurrently. Discussion focuses on the role of temperament-based mechanisms in the expression of prosocial behaviors in different contexts in adolescence.