This study examined the links between mothers' and fathers' emotion socialization practices and social behaviour between siblings. We utilized parent reports from 57 two-parent families with preschool- and toddler-aged siblings to assess parental responses to children's negative emotions, as well as siblings' engagement in positive involvement, conflict, and avoidance. Findings indicated that fathers', but not mothers', supportive and non-supportive emotion socialization strategies with the older sibling accounted for a significant amount of variance in older siblings' rivalry, aggression, and avoidance. Additionally, older siblings' rivalry/aggression and avoidance were positively linked to fathers' non-supportive reactions to both the older and younger siblings' negative emotions, highlighting the importance of a within-family approach to emotion socialization to elucidate effects across parents and siblings. Further research is needed to disentangle cause and effect relations among siblings' socio-emotional development and parents' emotion socialization practices.