Objective: The purpose of this study was to examine the relationships among young children's temperament, emotional regulation, and their mother's parenting stress. This study also analyzed the mediating effect of mother's parenting stress on the relationship between the other two variables. Methods: A total of 304 mothers with young children that lived in Gwangju and Jeollanamdo participated in this study. The data were analyzed using Pearson's correlation coefficient, hierarchical multiple regression analysis, and the Sobel test. Results: The main results are as follows. First, adaptability temperament was positively correlated with children's emotional regulation and negatively correlated with mother's parenting stress. There was no statistically significant relationship between activity temperament and other variables, whereas regularity temperament had only a significant relationship with emotional regulation. Second, it was found that mother's parenting stress partially mediated between children's adaptability temperament and emotional regulation. Conclusion: The results of this study imply that mother's parenting stress is a very important factor on young children's emotional regulation. Also, the present study suggests that children’s adaptability temperament and mother’s parenting stress should be considered together in order to improve young children’s emotional regulation.