Background: Numerous studies have examined the three dark traits of personality and aggression, But research that predicts aggression in sports based on the dark three personality traits of coaches and athletes has been neglected. Aims: The present study aimed to examine the effect of dark triad traits of personality on aggression of coaches and athletes. Method: The research method was descriptive-correlational. The statistical population in the present study included all coaches and athletes in Tehran in 1399, from which 80 participant (40 athletes and 40 coaches were selected via convenience sampling among the coaches and athletes of Tehran coaches and athletes in 2020. They completed questionnaires of Short Dark Triad (SDTS; Paulhus & Jons, 2010) and Aggression (AQ; Buss and Perry, 1992) competing. The data were collected and analyzed by Pearson correlation and multiple regression tests (Enter method) by SPSS version 25. Results: The results showed a significant relationship between Three dark personality traits (Narcissism, Machiavellianism and psychopathy) and aggression. Moreover, dark personality traits positively predicted aggression variance both coach and athlete. Conclusions: The results of this study indicate that that personality and its dark traits plays an important role in tendency to aggression of both coaches and athletes. Therefore, psychologists are advised to pay attention to these traits in the aggression of coaches and athletes in sports.