The inherent neural mechanism in prosocial behavior and its developmental trajectory are inadequately understood. To address the above gaps, a two-pronged empirical approach, such as experimental approach (e.g., evidence from event-related potentials) and longitudinal questionnaire approach (e.g., latent growth model), is urgently needed to depict a more complete picture of this phenomenon. While both the experimental approach and the correlational approach have their strengths and limitations, they complement one another. In study 1, I sought to replicate prior research and reexamine the relation between SES and adolescents' prosocial behaviors in the ERPs experiment. In study 2, I intend to establish empirical support for the interaction between economic inequality and SES on adolescents' prosocial behavior and the underlying neural mechanism. In these studies, I manipulate the economic inequality and SES in the laboratory experiment to draw causal inferences. Considering the limited external validity of the experiment, study 3 aims to provide longitudinal support for the processing mechanism that explains how economic inequality and SES affect the developmental trajectory of adolescents' prosocial behavior.