The aim of this short-term longitudinal study was to explore the moderating role of insecure mother--child attachment (i.e., ambivalent and avoidant) in the relations between shyness and indices of adjustment difficulties in early childhood. Participants were 360 children (200 boys and 160 girls, M[subscript age]=4.72 years, SD=0.63) attending preschools/kindergartens in Shanghai, People's Republic of China. At Time 1, mothers rated children's shyness and insecure attachment. At Time 2, 1½ years later, teachers assessed children's adjustment outcomes at school. Among the results, shyness was negatively associated with sociability, social competence, and internalizing problems. However, both ambivalent and avoidant insecure attachment significantly moderated these associations, exacerbating the relations between shyness and indices of adjustment difficulties. Results are discussed in terms of the contributions of attachment to young shy children's adjustment outcomes.