The present study aimed to investigate the relationship between need-supporting and non-need-supporting behaviors and self-esteem of Iraqi and Iranian athletes with the mediating role of positive psychology. This research is of an applied, quantitative and descriptive-correlational type. The statistical population of study was 148 volleyball athletes in the city of Karbala, Iraq, and the city of Tabriz, Iran, whose number was determined using GPower software and their selection method was accessible and purposeful. The data collection tools were the Lonsdale et al. Basic Needs in Sports Questionnaire (2007), the Bartholomew et al. Basic Needs in Sports Questionnaire (2011), the Crocker and Neuer Self-Esteem Questionnaire (2003) and the Rashid et al. Positive Psychology Questionnaire (2015). Data analysis was performed using descriptive analysis, Kolmogorov-Smirnov test, structural equation modeling, Sobel and independent t-test in SPSS version 23 and SmartPLS version 3.1.1 software at a significance level of 0.05. The results showed that need-supporting behavior has a direct relationship and non-need-supporting behavior has an inverse relationship with self-esteem and positive psychology (p<0.05), positive psychology has a direct and significant relationship with athletes' self-esteem (p=0.008), positive psychology acts as an increasing mediator in the relationship between need-supporting and athletes' self-esteem and as a decreasing mediator in the relationship between need-supporting and self-esteem (p=0.001) and there is no significant difference between need-supporting behaviors, self-esteem and positive psychology between Iraqi and Iranian athletes (p<0.05). Therefore, the contribution of psychological exercises related to meeting basic needs as well as positive thinking in volleyball athletes' training can be increased.