The goal of this study was to examine whether the security of the relationship between mothers and children influenced the relation between maternal emotional expressiveness and aspects of children's social development. Fifty-one preschool children (M age = 52.80 months) and their mothers took part in the study. At their homes, mothers completed the Attachment Q-set. At the lab, children completed a measure of their representations of family relationships, while mothers completed measures of maternal emotional expressiveness and reports of the child's social competence. Findings supported the idea that the quality of the attachment relationship moderated the influence of maternal positive expressiveness. For children who were low in attachment security, maternal positive expressiveness was an important predictor of representations of relationships. For those who were high in attachment security, maternal positive expressiveness was unrelated to social development. Overall, the pattern of findings suggests that high levels of maternal positive expressiveness may compensate for a lack of attachment security in promoting social development.