Objectives: This study's aim was to examine the importance of preschoolers' social competence and the effects of smart-media (smartphones, tablet PCs) use on the development of their social competence. Methods: Questionnaires were used to measure preschoolers' social competence, smart-media usage time, parents' media literacy, and smart-media mediation. SPSS 22.0 and AMOS 22.0 were used to analyze the collected data while descriptive statistics, t-test, Pearson's correlation, structural equation modeling, and bootstrapping were adopted for data analysis. Results: First, parents' media literacy had significant effects on their smart-media mediation, which in turn had indirect effects on preschoolers' smart-media usage time. Second, preschoolers' smart-media usage time had a significant effect on their social competence. Additionally, their parents' smart-media mediation indirectly affected their social competence through their smart-media usage time. Conclusion: The findings highlight the importance of parental roles in mediating and regulating preschoolers' use of smart-media to promote their healthy social development.