This study examined the role of mother-son emotional reciprocity in connections between marital conflict and the quality of boys' peer relationships. Parents from 84 intact families with preadolescent boys reported on the level of conflict in their marital relationship. Observations of mother-son interaction were coded for emotional reciprocity, and assessments of boys' peer relationships were obtained from both teachers and classmates. No direct connection between marital conflict and boys' peer relationships was observed. Rather, marital conflict affected boys' social competence indirectly, through its effect on the emotions expressed between mother and son. The findings support the proposal that emotional processes play an important role in connections between marital conflict and children's peer relationships and suggest that family emotional expressiveness deserves greater attention in both research and intervention.