Most of the previous research has been focused mainly on the effects of parent-child relationships and marital relationships on adolescent development. The purpose of the present study is to investigate the potential impacts of the sibling relationship, another important family subsystem that also has significant influences on adolescent development, across early and middle adolescence.;Three theoretically interested models, the stress-suppressing model, the counteractive model, and the buffering model, were tested by structural equation modeling (LISREL VIII), using the three-wave data collected from multiple informants (fathers, mothers, target children, and siblings). Positive sibling relationships in adolescence were hypothesized to predict fewer adolescent developmental problems later, directly and indirectly through adolescent friendships, academic achievement, and self-esteem. Positive sibling relationships in adolescence were also hypothesized to have buffering effects on later adolescent development. Adolescents with higher level of perceived positive sibling relationships should have fewer developmental problems than those who face the same risk factors but do not have positive sibling relationships.;Results showed that early positive sibling relationships influence adolescent development only indirectly through adolescent friendship quality and self-esteem. Adolescents who perceived more positive sibling relationships at Time 1 tend to have better friendships and higher self-esteem at Time 2, which in turn lead to higher self-esteem, less loneliness, less depression, and fewer delinquent behaviors and substance uses later at Time 3. Moreover, a bidirectional relationship was found between adolescent self-esteem and their sibling relationship quality, suggesting that higher level of positive sibling relationships help to enhance adolescent self-esteem, and higher adolescent self-esteem predicts higher level of positive sibling relationships.;Furthermore, a significant positive relationship was found from adolescent positive sibling relationships at Time 1 to adolescent friendships at Time 2, not from adolescent friendships at Time 1 to adolescent positive sibling relationships at Time 2. It suggests that earlier sibling relationship quality is more predictive of later friendship quality for adolescents, rather than the other way around. The implications and limitations of the present study were discussed to explain and emphasize the importance of positive sibling relationships on adolescent development.