Background: We investigated attachment behaviours of children with Down syndrome (DS) toward their preschool teacher and examined whether children's emotional expressivity predicted the incidence of attachment behaviours. We hypothesised that children with DS will show a low level of secure attachment to their teacher and that emotional competence will be associated with secure attachment. Method: Forty-one children with DS (21 males, 20 females, M mental age = 34.6 months, SD = 11.9) were matched with 51 typically developing (TD) children (24 males, 27 females, M mental age = 32.2 months, SD = 17.5). Attachment and socio-emotional development were assessed for each child. Results: Children with DS presented lower scores of attachment, affiliation, anger, and emotional competence compared to TD children. Affiliation in high-stress situations was predictive of attachment behaviours. Conclusions: The findings show that children with DS were less attached to the teacher and less emotionally expressive compared to TD children.