Attachment theory states that emotion regulation is one of the central features of attachment system. The current study adopted an attachment perspective to investigate how mother-child attachment at 36 months and teacher-child relationships at 54 months influence children’s emotion regulation in 3rd grade, and whether teacher-child relationships moderate the associations between mother-child attachment and children’s emotion regulation. Longitudinal data from the first three phases of the National Institute of Child Health and Human development Early Child Care Research Network of Study of Early Child Care and Youth Development (NICHD SECCYD) were used in the study. The results showed that the association of teacher-child conflict and child’s negative engagement with peers was statistically significant. Additionally, teacher-child relationships significantly moderated the impacts of mother-child attachment on children’s emotion regulation. Specifically, the relationship between teacher-child conflict and negative engagement with peers for children with secure attachment and for those with disorganized attachment were in opposite directions. The relationship between teacher-child closeness and negative engagement with peers was significant for children with disorganized attachment, but not for children with secure attachment. And, the results showed that the levels of conflict in teacher-child relationships for children with ambivalent and with disorganized attachment were statistically different from those for children with secure attachment. The present study fills in the research gap with regard to the effects of teacher-child relationships on children’s emotion regulation. It also suggests that children’s experiences of positive teacher-child relationships may compensate for the negative impacts of insecure early mother-child attachment patterns on emotion regulation development.