This study tested potential mediating effects of household screen media experience (HSME) on the relationship between SES and six aspects of preschooler's sociality: social cognition, independence, aggression, social adaptivity, peer relationship and emotional control. A total of 471 parents of 3- to 6-year-old children completed an online questionnaire on SES, household screen media experience and social behaviours of children. Our results revealed that the effects of SES on Social Cognition, Independence and Aggression were partly mediated by HSME. Specifically, higher SES predicted lower HSME scores, which predicted better Social Cognition, higher Independence and lower Aggression. HSME did not appear to mediate the effects of SES on Social Adaptivity, Peer Relationship, and Emotional Control. This study affords novel insights into the role of screen use in children's sociality development.