This study evaluated whether children's emotional display rule behavior and gender moderated associations between mothers' affective balance and preschoolers' (46 boys, 44 girls) social initiations and prosocial behavior, which were assessed using semi-naturalistic observational methods. Seventy-three of the dyads were White and 17 were Asian. The association between mothers' affective balance and prosocial behavior was positive for children high in emotional display rule behavior and negative for children who were low in this behavior. Associations between mothers' affective balance and social initiations and prosocial behavior were negative, but only for boys. In contrast, the relation between mothers' affective balance and prosocial behavior was positive for girls. Findings can inform parent and child-focused interventions targeting parental socialization of emotion and its role in young children's peer competence.