The purpose of this study is confirming the mediating effect of multidimensional aggression on the effect of adult attachment on relationship satisfaction. Due to this, a questionnaire was conducted on adult attachment, relationship satisfaction, and multidimensional aggression targeting 223 adult men and women. This collected data analyzed the relationship between adult attachment and relationship satisfaction and the mediating effect of aggression and the parallel mediating effect of multidimensional aggression through the SPSS process macro model 4. The main results are as follows. First, the higher the attachment anxiety and attachment avoidance, the lower the satisfaction in the relationship. Second, the higher attachment anxiety and attachment avoidance had a positive effect on aggression. Third,aggression was found to mediate between attachment anxiety and relationship satisfaction, and attachment avoidance and relationship satisfaction. Lastly,in the sub-factors of aggression, the mediating effect of hostility was the largest. We found that intervention in aggression, especially hostility, is important in promoting relationship satisfaction. Based on the results of this study, we present an intervention method to increase relationship satisfaction,and specify the limitations of this study.