In addition to a number of differences, different group sports have some certain common elements. It is achieving the best possible result, but also the existence of a leader in the team. The role of team leader is characteristic and important feature of all group sports. In addition to a team leader who is associated with many positive factors in sports, the mood of athletes, collective efficiency and group cohesion are also very important. Therefore, the aim of this research is to examine the role of team leader between group cohesion, collective efficacy and mood in athletes. The study involved 213 (n=213) male athletes (n=139) and female athletes (n=74) aged 18 to 67 years (M = 23,65; SD = 5.851). Respondents solved constructed team leader questionnaire, POMS – Profile of Mood States Questionnaire, GEQ - Group Environment Questionnaire, Ocess - collective efficacy questionnaire and general dana questionnaire. The results showed a significant mediating role of the leader on the relationship with both dimensions of group cohesion (individual attraction to the group and group integration) and collective effectiveness. More pronounced group cohesion (individual attraction to the group and group integration) results in a more pronounced role of the leader, which results in greater collective effectiveness. Also, the results showed a significant mediating role of the leader on the relationship between group integration and mood factors Numbness and Fatigue. More specifically, pronounced group integration leads to a more pronounced role of the leader, which results in a greater numbness and fatigue. Also, the partial mediating role of the leader in the relationship between collective efficiency and the Fatigue was shown. A more pronounced collective efficiency results in a more pronounced role of the leader, which results in greater fatigue.