The negative impact of political violence on adolescent adjustment is well established. Less is known about factors that affect adolescents' positive outcomes in ethnically divided societies, especially influences on prosocial behaviors toward the out-group, which may promote constructive relations. For example, understanding how inter-group experiences and attitudes motivate out-group helping may foster inter-group co-operation and help to consolidate peace. The current study investigated adolescents' overall and out-group prosocial behaviors across two time points in Belfast, Northern Ireland (N = 714 dyads; 49% male; Time 1: M = 14.7, SD = 2.0, years old). Controlling for Time 1 prosocial behaviors, age, and gender, multi-variate structural equation modeling showed that experience with inter-group sectarian threat predicted fewer out-group prosocial behaviors at Time 2 at the trend level. On the other hand, greater experience of intra-group non-sectarian threat at Time 1 predicted more overall and out-group prosocial behaviors at Time 2. Moreover, positive out-group attitudes strengthened the link between intra-group threat and out-group prosocial behaviors one year later. Finally, experience with intra-group non-sectarian threat and out-group prosocial behaviors at Time 1 was related to more positive out-group attitudes at Time 2. The implications for youth development and inter-group relations in post-accord societies are discussed.