Objective: The purpose of this study was two-fold: first to explore the effects of mother-child attachment and effortful control at age 1 on preschoolers school readiness at age 6, and second, to determine the mediating effect of a child s effortful control on the relationship between mother-child attachment at age 1 in relation to school readiness at age 6. Methods: Participants in this study were 205 five-year-old toddlers(106 boys, 99 girls) recruited for the Korea Child Panel Study. Mother-child attachment was assessed using the Attachment Q-sort(Waters, 1989). Preschooler s effortful control was measured by the Early Childhood Behavior Questionnaire: ECBQ(Putnam, Gartstein & Rothbart, 2006). Preschooler s school readness was measured by the School Readiness Scale Murphey & Burns, 2002). Data were analyzed using descriptive statistics, correlations, and the structural equation modeling analysis. Results: First, mother-child attachment at age 1 effected school readiness at age 6. Effortful control at age 1 effected school readiness at age 6. Second, effortful control at age 1 mediated the effect of mother-child attachment at age 1 in relation to school readiness at age 6. Conclusion/Implications: Mother-child attachment at age 1 affects school readiness at age 6, and toddlers effortful control at age 1 mediates the relationship between mother-child attachment in relation to school readiness at age 6.