The purpose of this study is to analyze the mediating effect of service quality satisfaction in the relationship between the quality of volunteer service and social capital formation. For this purpose, hierarchical regression analysis and structural equation model are used. The main results are as follows. First, overall service satisfaction and service use are found to have a significant impact on social capital, indicating that users' social capital increases with higher overall service satisfaction and higher usage. Second, among the impacts of volunteer service quality on social capital, responsiveness has a direct significant impact on social capital, and reliability, certainty and empathy are not directly significant. Third, the overall service satisfaction has a mediating role between the quality of volunteer service and the social capital of the users, confirming that the quality of volunteer service increases social capital through overall service satisfaction. In particular, empathy, reliability, and certainty affect social capital through overall service quality satisfaction, thus the overall service satisfaction has the full-mediating effect between the quality of volunteer service and the social capital of the user. Based on these findings, this study presents theoretical and practical implications for increasing social capital of volunteer users.