Implicit theories provide a framework for understanding events and for interpreting and predicting the world. This research examines how implicit theories influence prosocial behavior which is an intentional act undertaken to enhance the welfare of others or society as a whole. Consistent with an intuition that individuals holding a fixed view (i.e., entity theorists), as compared to those holding a malleable view (i.e., incremental theorists), are less motivated to engage in prosocial behavior, studies 1a and 1b show that entity (vs. incremental) theorists have lower tendency to participate in the recycling initiative which is beneficial to society as a whole (study 1a), and are less willing to donate to the charitable organization which helps others in need (study 1b). However, study 2 demonstrates that it is not always the case. We show that even entity theorists are more motivated to engage in prosocial behavior when beneficiaries are their group members than when they are outgroup members. In contrast, incremental theorists are highly motivated to engage in prosocial behavior regardless of whether beneficiaries are ingroup members or not. We also demonstrate that the interaction effect of implicit theories and group membership is mediated by the perceived effectiveness of prosocial behavior. Specifically, since entity theorists (vs. incremental theorists) are more motivated to enhance themselves and more inclined to describe them in terms of social identity, they strive to self-enhance by improving their group images. Hence, entity theorists perceive prosocial behavior for ingroup members more effective than that for outgroup members. In contrast, incremental theorists’ perceived effectiveness of prosocial behavior is not influenced by group membership.