The present study was conducted with the aim of investigating the relationship between secure, avoidant, and ambivalent attachment styles and aggression in students of Islamic Azad University, Shiraz Branch. Based on the theoretical foundations of attachment, early emotional patterns are expected to play an important role in emotion regulation and the emergence of interpersonal behaviors; therefore, aggression, as one of the important emotional outcomes in adolescence, can be affected by these styles. This descriptive-analytical and cross-sectional correlational study was conducted on 269 students who were selected using a multistage cluster sampling method. Data collection tools included the Bass and Perry Aggression Questionnaire and the Hazan and Shaver Attachment Style Questionnaire. The data were analyzed using the Pearson correlation test and simultaneous multiple regression. The results showed that there is a negative and significant relationship between secure attachment and aggression, and a positive and significant relationship between avoidant and ambivalent attachment and aggression. Also, attachment styles explained a total of 27% of the variance in aggression; so that secure and avoidant attachment were significant predictors of aggression, but ambivalent attachment did not have a significant predictive power. Based on the results, it can be concluded that attachment style plays an important role in explaining aggressive behaviors of students, and strengthening secure attachment and emotion regulation skills can help reduce aggression and improve their social adjustment.