The study examined the relation between the security of attachment and trust beliefs in close others during middle childhood. In the study, 133 children (63 girls, M age = 9.5 years) completed standardized measures of the security of attachment and three bases of trust beliefs in close others (reliability, honesty, and emotional). Correlational analyses showed that children's security of attachment was associated with emotional trust beliefs in close others only. A structural equation modelling analysis yielded a path between security of attachment and emotional trust beliefs in parents as a latent factor. In addition, there was a path between the latent factor and emotional trust beliefs in peers. Alternative models did not adequately fit the data. The findings were ascribed to the role of parent's emotional trustworthiness and children's mental state discourse in promoting the relation between children's security of attachment and their emotional trust beliefs in close others. K E Y W O R D S close others, middle childhood, secure attachment, trust beliefs Highlights • The research examined relation between the security of attachment and trust beliefs in close others during middle childhood. • One hundred and thirty-three children completed standardized measures of the security of attachment and trust beliefs in close others.• Children's beliefs that parents refrain from causing emotional harm play a central role in their security of attachment.