This study aims to investigate the effect of childhood attachment trauma experiences on relational aggression and to confirm the mediating effect of hostile attribution bias. To this end, this study conducted an online self-report survey of adults in their 20s and 30s living in Korea. For data analysis, the average, standard deviation, frequency analysis, Pearson’s correlation analysis, stepwise multiple regression analysis, simple regression analysis, and bootstrapping were performed using the SPSS 22.0 statistical program and the SPSS Process Macro 4.1 program. The results of this study are as follows. First, as a result of correlation analysis, there was a positive correlation between childhood attachment trauma experience, hostile attribution bias, and relational aggression. Second, as a result of verifying the mediating effect, it was found that the partial mediating effect of hostile attribution bias was significant in the relationship of relational aggression in childhood attachment trauma experience. Therefore, this study is expected to contribute to therapeutic interventions to form adaptive relationships among adults with childhood attachment trauma experiences by identifying new paths mediated by hostile induction bias about child attachment trauma experiences and relational aggression.