The aims of this study were to investigate the relationships among mothers’emotion expression, preschool children’s temperament, and preschool children’s emotion regulation. The participants in this study were 75 5-year-old children from five child-care centers located in Seoul. The collected data were analyzed using simple regression and hierarchical multiple regression. The major findings were as follows. First, mothers’positive emotion expression had a positive influence on children’s effortful control, and mothers’negative emotion expression had a positive influence on children’s negative affect. Second, mothers’ positive emotion expression had a positive influence on children’s emotion regulation, while mothers’negative emotion expression had a negative influence on children’s emotion regulation. Last, the effect of mothers’positive emotion expression on children’s emotion regulation was fully mediated by children’s effortful control. Also, the effect of mothers’negative emotion expression on children’s emotion regulation was partially mediated by children’s negative affect. These results suggest that mothers’emotion expression and children’s temperament may predict children’s emotion regulation.