Despite a growing awareness of the detrimental effects of economic inequality, less is known about whether adolescents' perception of economic inequality relates to their long-term development. This study examined the relations between perceived economic inequality, system justification, and prosocial behavior in a three-wave longitudinal study among 1,525 Chinese adolescents (50.1% boys; Mage at Wave 1 = 12.47 years, SD = 0.69). Results from cross-lagged panel models revealed that perceived economic inequality predicted less prosocial behavior, and system justification mediated this association. System justification also predicted lower perceived economic inequality longitudinally. These findings enrich our understanding of the macro-level economic factors as predictors of prosocial behavior and highlight the negative effects of economic inequality on adolescents' social development.