The purpose of this study was to comparison the dark triad traits of personality, cognitive decision making and mental toughness in natural, supplement and steroid bodybuilders. The method of this research is causal-comparative descriptive. The statistical population of the study consisted of all natural, supplement and steroid bodybuilders in Rasht (2019) among whom 150 individuals (50 natural bodybuilders, 50 supplement bodybuilders and 50 steroidal bodybuilders) were selected and available on a Dark Triad Traits of Personality Scale Jonsson and Webster, Iowa Gambling Task Scale, and Sports Mental Toughness Questionnaire Sheard et al. Multivariate analysis of variance and LSD test were used to analyze the data. Results of multivariate analysis of variance showed that there was a significant difference between dark triad traits of Personality, cognitive decision making, and mental toughness in the three groups. Also, the results of the LSD follow-up test showed that steroid bodybuilders had more dark triad traits of personality and loss of body traits compared to natural and supplement bodybuilders and had less mental toughness and won. Based on the findings of the present study, it can be concluded that abuse of steroidal drugs has detrimental effects on personality and psychological characteristics of athletes. So, coaches need to pay more attention to these issues.