Objective: The purpose of this study was to examine the relationships among maternal autonomy support, preschoolers' executive function, and preschoolers' emotional and social competence. In addition, the mediating role of preschoolers' executive function between maternal autonomy support and preschoolers' emotional and social competence was investigated. Methods: A total of 245 preschoolers (130 boys and 115 girls) and their mothers participated in this study. Data were collected through maternal reports. Results: First, maternal autonomy support was significantly related to preschoolers' emotional and social competence. Second, maternal autonomy support was significantly related to preschoolers' executive function. Third, preschoolers' executive function was significantly related to emotional and social competence. Fourth, preschoolers' executive function partially mediated the relationship between maternal autonomy support and preschoolers' emotional and social competence. Conclusion: These results highlight the importance of executive function in attaining emotional and social competence during the preschool period.