The purpose of this study is to examine how entity belief of personality contribute to university students’ depression and reactive aggression. In this process, hostile attribution bias was considered as a mediator. As a result of structural equation modeling, it was found that the relationship between entity belief of personality and depression was partially mediated by the hostile attribution bias, and the relationship between entity belief of personality and reactive aggression was completely mediated by the hostile attribution bias. In other words, a strong belief that a person's attributes do not change not only directly predicts depression, but also creates a cognitive bias that interprets the intentions of others as hostile, leading to depression. On the other hand, it was found that entity belief of personality increases reactive aggression only through the process of increasing the hostile attribution bias. Through this study, the role of hostile attribution bias in the relationship between entity belief of personality, depression, and reactive aggression was confirmed, and implications for new strategies to reduce depression and reactive aggression were discussed.