Considering that the satisfaction and success of athletes are defined by numerous psychosocial factors, the goal of this research is to examine the contribution of mental toughness and social support to success and satisfaction of young adult athletes. The research has been conducted on a total of 81 female (N = 18) and male (N = 63) athletes, age ranging from 17 to 30 (M = 21,36; SD = 3,70). The participants have filled in the Sports Mental Toughness Questionnaire, Multidimensional Scale of Perceived Social Support and a Satisfaction Scale for Athletes. Their coaches have evaluated them through the Indicators of Sports Performance. The results have shown that constancy, as a dimension of mental toughness, significantly contributes to success of young adult athletes. Furthermore, the results have shown a positive and a significant contribution of social support that stems from family and friends to life satisfaction of young adult athletes. Social support that stems from the significant other and it's contribution to life satisfaction of young adult athletes has shown to be significant and negative. Finally, the results have also shown that social support moderates the relationship between constancy as a dimension of mental toughness and success. Precisely, the constancy significantly contributes to a higher rate of success on the middle and higher level of social support, but doesn't significantly contribute to a higher rate of success on the lower level of social support.