This study examined the structural relations of preadolescents' inattention and hyperactivity/impulsivity, aggressive and prosocial behaviors, and peer functioning. There were 739 fourth (n = 239) and fifth (n = 500) graders (52.23% boys) in Taiwan who participated in this study. Preadolescents' inattention and hyperactivity/impulsivity were assessed using parent reports on the Swanson, Nolan, and Pelham IV Rating Scale. Aggressive behaviors, including physical aggression and relational aggression, and prosocial behaviors were assessed using teacher and peer reports. Peer acceptance and the number of reciprocated friendships were obtained through peer nomination administered 6 months later after initial assessment and were combined to assess children's peer functioning. Results of structural equation modeling demonstrated that inattention was indirectly linked to impaired peer functioning through low levels of prosocial behavior, regardless of gender. In addition, inattention was directly related to less optimal peer functioning only for girls. Hyperactivity/impulsivity was neither directly nor indirectly related to impaired peer functioning in boys, although it was related to more physical and relational aggression. However, for girls, a positive and direct path existed between hyperactivity and peer functioning. Further, hyperactivity in girls was associated with more physical aggression, which in turn led to poorer peer functioning. These findings suggested that the processes related to each core domain of ADHD and peer functioning may be varied, depending on the mediating factors (e.g., aggression or prosocial behavior) and gender.