The purpose of the study was to investigate the mediating effects of emotion regulation strategy on the relationships between rejection sensitivity and quality of peer relationships of late school-aged children. For this, data was collected from total 355 elementary school students in 5th and 6th grades. The collected data were analyzed by t-test, Pearson’s correlation and multiple regression analysis using SPSS 22.0. The major results of this study were as follows. First, while there was no gender difference in emotion regulation strategy, rejection sensitivity and quality of peer relationships of girls was higher than boys. Second, rejection sensitivity was negative correlation with emotion regulation strategy and quality of peer relationships, emotion regulation strategy was positive correlation between quality of peer relationships but rejection sensitivity was not correlation with experiential emotion regulation strategy in case of boys. Third, emotion regulation strategy was partially mediated the relationships between rejection sensitivity and quality of peer relationships but experiential emotion strategy was not mediated the relationships between rejection sensitivity and quality of peer relationships in case of boys. This study is significant in terms of identifying gender difference about mediation effects of emotion regulation strategy between rejection sensitivity and quality of peer relationships of late school-aged children.