Objective: The purpose of this study is to analyze the mediating effects of mother’s smartphone addiction on the relationship between mothers’ parenting stress and young children’s smartphone addiction. Methods: This study conducted a survey targeting a total of 327 mothers with young children between the ages of 3-5 years that were attending kindergartens and daycare centers in Gyeonggi-do, Gangwon-do, and the Busan region. After exploring the relationship between mothers’ parenting stress, mothers’ smartphone addiction, and young children’s smartphone addiction based on the collected data, this study comparatively analyzed the complete mediation and partial mediation models by using the structural equation. Results: The mothers’ smartphone addiction played a partial mediating role in the relationship between mothers’ parenting stress and young children’s smartphone addiction. In other words, the mothers’ parenting stress and mothers’ smartphone addiction were important variables for young children’s smartphone addiction. Conclusion/Implications: This study aims to provide basiv data for the prevention of problems caused by young children’s smartphone addiction, by exploring the paths of mothers’ parenting stress and mothers’ smartphone addiction which have effects on young children’s smartphone addiction.