Abstarct: The purpose of this study was to investigate the effect of mindfulness on the mental toughness of volleyball plaxyers with the mediating role of perceived social support. The research method was descxriptive-correlational in nature and cross-sectional in terms of time. The statistical population of the study included all volleyball plaxyers in Semnan province, and 236 individuals were selected as the sample using convenience sampling. The research instruments consisted of three standardized questionnaires: the Mental Toughness Questionnaire by Dagnal et al. (2019), the Sport Mindfulness Questionnaire by Sinnot et al. (2014), and the Perceived Social Support Questionnaire by Zimet & Farley (1998). To assess the face and content validity of the research tools, the opinions of ten experts in sports management were utilized, and the reliability of the instruments was confirmed using Cronbach's alpha. Structural equation modeling with a variance-baxsed approach was employed to examine the research hypotheses. Data analysis was performed using SPSS23 and Smart-PLS 4 software. The results indicated that mindfulness has a direct and significant effect on mental toughness and perceived social support among volleyball plaxyers in Semnan province. Additionally, the findings showed that perceived social support has a direct and significant impact on the mental toughness of these plaxyers. The mediating role of perceived social support in the relationship between mindfulness and mental toughness was also confirmed. Mindfulness, by enhancing plaxyers' capacity to effectively perceive and receive social support, provides a suitable foundation for strengthening mental toughness. This dual effect highlights the importance of multi-level interventions in sports psychology that focus on both individual development and improving group dynamics. Such findings can serve as a scientific basis for designing more comprehensive psychological preparation programs for athletes, emphasizing both the enhancement of individual mindfulness and the improvement of team relationship quality.