Materialism plays a critical role in adolescent behavioral development, yet whether it affects prosocial and aggressive behaviors and the internal mechanism remains unknown. Therefore, this longitudinal research examined the relationships between adolescent materialism and prosocial and aggressive behaviors, and tested the mediating effect of empathy. In 2015, we recruited 543 adolescents from four junior high schools in Beijing, China (284 girls, 259 boys; M = 11.27 years, SD = 0.51). The participants completed the measures of materialism and demographic information at the initial time point, completed the measure of empathy about one year later, and completed the measures of prosocial and aggressive behaviors after about another year. The hypotheses were tested using a structural model using maximum likelihood estimation. The mediating effects were estimated by taking 1000 bias-corrected bootstraps. The results revealed that materialism was associated with aggressive behavior directly and positively, but had no significant correlation with prosocial behavior. Materialism had an indirect and negative correlation with prosocial behavior via empathy, while no indirect effect of materialism on aggressive behavior was found. The findings add to our knowledge of the dehumanizing nature of materialism by revealing its effect on adolescent behavioral development, as well as the underlying mechanism.