Purpose: The purpose of this study was to reveal the formation process by depth approaches to mental toughness of elite Ssirum players. For this purpose, we used grounded theory approach that was widely used qualitative analysis. Methods: We selected elite Ssirum players as participants who had champion title by association of professionals that was composed of Ssirum experts and sports psychologists. To gather material for formation process of mental toughness, we used in-depth interview, non-participant observation and leaders interview, and by triangulation, confirmation of participants and consultation of experts, we had enough validity. All of data were analyzed for interactions of cause and effect, context relationship, mediation qualification and interactive strategy. Results: The process mental toughness of elite Ssirum players was divided into 4 stages : creating champion goals by positive expectation, social support by parents and leaders, constant effort with positive feedback by leaders, development of personal mental toughness by individual experience. Conclusion: These results might provide information to develop new related theories by revealing the formation factors of mental toughness, which might improve the Ssirum leaders and young players' performance.