Objective: This study examined the mediating roles of preschoolers self-regulation in the relationship between maternal parenting behaviors and preschoolers excessive immersion in smartphones. Methods: A total of 268 mothers of preschoolers responded to questionnaires on three research variables. Data were analyzed by correlation analyses and regression analyses. Results: First, maternal warmth/encouragement was negatively related to preschoolers excessive immersion in smartphones, while maternal overprotectiveness/ permission and rejection/neglect were positively related to preschoolers excessive immersion in smartphones. Second, maternal warmth/encouragement and limit setting were positively linked to preschoolers self-regulation, but maternal overprotectiveness/permission and rejection/neglect were negatively linked to preschoolers self-regulation. Third, preschoolers self-regulation was negatively associated with their excessive immersion in smartphones. Finally, preschoolers self-regulation fully mediated the relationship between maternal warmth/encouragement and preschoolers excessive immersion in smartphones, and preschoolers self-regulation partially mediated the relationship between maternal overprotectiveness/permission, rejection/neglect and preschoolers excessive immersion in smartphones. Conclusion/Implications: The results of this study suggest that positive maternal parenting behaviors and preschoolers effective self-regulation are important in order to decrease preschoolers smartphone overuse. These findings provide empirical evidence to develop programs for prevention and intervention of preschoolers’ smartphone addiction.