The purpose of this study was to examine the effects of parenting behavior and peer interaction on externalizing problem behaviors of preschoolers. The data of 953 49~55 month old preschoolers and their parents were extracted from the Korean Children Panel Survey of Child-Care Policy Research Institute(2012). This study was conducted with Structural Equation Modeling(SEM). The results of this study were as follows. First, parenting behavior had a direct influence on externalizing problem behaviors of preschoolers. Second, parenting behavior had a direct influence on preschoolers' peer interaction. Third, preschoolers' peer interaction had a direct influence on externalizing problem behaviors of preschoolers. Fourth, preschoolers' peer interaction had mediating effects on the relationship between parenting behavior and externalizing problem behaviors of preschoolers.