Abstarct: The present study investigated the effect of serious leisure time on the quality of life with the mediating role of subjective well-being of student athletes. The research method was descxriptive and correlational. The statistical population of the study included 508 male student athletes in the second high school of Kashmar city, and 208 people were selected as a statistical sample using the available non-random sampling method. The standard questionnaires of serious leisure time by Gould et al. (2008), quality of life by Bolling et al. (2013), and subjective well-being by Ventura-Leon et al. (2025) were used to collect the required information. For validity, face and construct validity were used, and reliability was obtained through Cronbach's alpha coefficient for the serious leisure time questionnaire by Gould et al. (0.8920), quality of life by Bolling et al. (0.9281), and subjective well-being by Ventura-Leon et al. (0.8402). The results of structural equations with PLS software showed that serious leisure time does not have a significant effect on the quality of life with the mediating role of subjective well-being of student athletes in Kashmar city, but serious leisure time has a significant effect on the quality of life, but serious leisure time does not have a significant effect on subjective well-being. Also, serious leisure time does not have a significant effect on the quality of life of students in Kashmar city with the mediating role of subjective well-being. Finally, it is suggested that since subjective well-being did not have a mediating role, it means that nothing has been done in schools to improve subjective well-being. Therefore, schools should design regular, sports, and voluntary programs that encourage students to participate actively and purposefully in order to improve their subjective well-being and quality of life by increasing their sense of competence and autonomy. Also, future studies should examine the effect of continuing serious leisure activities on subjective well-being and quality of life over longer periods of time to determine the sustainability of these effects.