Children's relationships with adults (e.g. parents and teachers) and within-family relationships (e.g. parent-parent) are important drivers for the development of children's social competence. The current study examined the contributions of adult-child relationships (parent-child and teacher-child) and parent-parent relationships to preschool children's social competence. In addition, the moderating roles of teacher-child relationships between parent-child and parent-parent relationships, and children's social competence were examined. Participants were parents and teachers of 127 children (M = 54.65, SD = 9.22 months) from Turkey. Parents reported on parent-child and parent-parent relationships and teachers reported on teacher-child relationships and children's social competence. Hierarchical regression models accounting for the nesting structure of the data were run to test the hypotheses. Results showed that teacher-child closeness was positively and teacher-child conflict was negatively associated with children's social competence. Parent-child and parent-parent relationships were not associated with children's social competence. Teacher-child closeness moderated the association between parent-parent conflict and social competence. The findings highlight the importance of examining both parent-parent and teacher-child relationships in the prediction of children's social competence.