Habitual or unreasonable jealousy over friends is linked to various psychological and social relationship problems in children and adolescents. Given that friendship jealousy involves one’s relationship with a friend and at least one or more peers, social contextual factors should play a role in friendship jealousy. Yet the current understanding of the contributors to friendship jealousy is limited to personal characteristics. The purpose of the current study was to explore the role of social contextual factors in young adolescents’ friendship jealousy and peer reputations for friendship jealousy, with focus on the target’s friendship network and the best friend’s network (i.e., rival network). It was hypothesized that the size of the friendship network, the size of the rival network, the number of outgroup rivals (i.e., rivals who do not consider the focal individual a friend), and the proportion of outgroup rivals in the best friend’s network (i.e., marginality) would predict vulnerability to jealousy over the best friend independently and interactively with self-esteem. It was also hypothesized that these network factors would predict peer reputations for friendship jealousy for those who were vulnerable to jealousy. Unexpectedly, none of the network factors predicted vulnerability to friendship jealousy. Also, three of the network factors failed to predict reputations for jealousy, but marginality yielded a significant result. Jealousy-prone individuals were more likely to earn reputations for friendship jealousy only when they had low marginality. This is the first study to examine and display the role of a social contextual factor in young adolescents’ peer reputations for friendship jealousy.