The purpose of this study was to investigate the mediating effects of emotional regulation ability on the relationships between mother-child communication styles and peer relationships between children. The participants were 527 children in the fifth and sixth grades of elementary school. They completed the measures of the Parent-Adolescent Communication Inventory, Emotional Regulation Scale and the Peer Competence Scale. The data was then analyzed by multiple regression analysis through SPSS. Also, a structural equation analysis was conducted using AMOS to find out the mediation effects. The results of this study are shown as follows: First, the children``s perception of the mother-child open communication style had significant effects on their peer relationships. Second, emotional regulation had significant effects on peer relationships. Third, emotional regulation ability mediated the effects of the mother-child communication style on peer relationships between children. It was found that the mother-child communication style influenced on peer relationships indirectly through emotional regulation.