The main purpose of the study was to examine the moderating role of the insecure mother–child attachment in the relations between social withdraw and peer difficulties. Participants were 487 urban children (247 boys, 240 girls) in elementary schools in Shanghai, the People’s Republic of China. Data on attachment-relevant coping styles in insecure relationships with mother were collected from children’s self-reports. Information concerning social withdrawal (i.e., shyness and unsociability) and peer difficulties (i.e., peer victimization and rejection) was obtained from peer nomination. Among the results, both shyness and unsociability were positively related to peer victimization and rejection. However, several interaction effects were also observed. Both avoidant and ambivalent attachment served an exacerbating role for peer difficulties for shy and unsociable children, with these patterns differing by gender. Implications for the contributions of attachment to socially withdrawn children’s peer adjustment are discussed.