This study examined if the effect of family functioning on preschoolers’ school readiness can be mediated by mothers’ affective parenting and preschoolers’ self-regulation in the year before children enter elementary school. This study analyzed the 7^th year data of panel study of Korean children collected by the Korean Institute of Child Care and Education. Statistical analysis included 1,513 pairs of 6-year-old children and mothers. Descriptive statistics analysis, correlation analysis, structural equation modeling, and bootstrapping analysis were conducted using SPSS 22 and Amos 20. The primary findings were as follows. First, the sub-factors of preschoolers’ school readiness composed of children’s social and emotional development, approach to learning, cognitive development and general knowledge, and communication were positively correlated with family functioning, mothers’ affective parenting, and preschoolers’ self-regulation. Second, the result of structural equation modeling showed that the indirect paths from family functioning to preschoolers’ school readiness through mothers’ affective parenting and preschoolers’ self-regulation were significant, while the direct path was insignificant. Third, bootstrapping analysis showed that mothers’ affective parenting and preschoolers’ self-regulation fully mediated the relationship between family functioning and preschoolers’ self-regulation. The findings provide the grounds for families and parents with preschool aged children to implement effective support practices to maintain a functional family system that can promote preschoolers’ school readiness.