The current study examined the associations between low-income preschool children's temperament (reactive and regulatory) and their relationships with parents and teachers. In particular, we focused on the moderating role of regulatory temperament on reactive temperament in the prediction of closeness and conflict with parents and teachers. Two hundred ninety-one children ([mean] = 53.88 months, SD = 6.44 months), their parents, and teachers from 3 different preschools serving low-income children in 2 midwestern cities in the United States participated. Parents reported on temperament and parent-child relationships, and teachers reported on teacher-child relationships. Hierarchical regression models using SAS PROC MIXED were employed to allow for nesting of children within classrooms. After controlling for child age, gender, ethnicity, and parent education, children's reactive temperament was negatively associated with parent-child closeness and positively associated with parent-child conflict and teacher-child conflict. Children's regulatory temperament was positively related to teacher-child closeness and negatively associated with teacher-child conflict. Regulatory temperament moderated the association between reactive temperament and teacher-child closeness. These findings suggest that although reactive temperament potentially undermines closeness in relationships with teachers, regulatory temperament can buffer the influence of reactive temperament on teacher-child closeness. Highlights: - This study examined the association between children's temperament and their relationships with parents and teachers. - Reactive temperament was positively associated with parent/teacher-child conflict and negatively associated with parent-child closeness. Regulatory temperament was a moderator for the association between reactive temperament and teacher-child closeness. - Improving children's regulatory temperament may be helpful for children with the reactive temperament to have better social relationships with their teachers. (author abstract)