Based on the social capital theory, this study investigated the effects of gender differences on the relationship of social capital and well-being among medical volunteers in Tzu Chi Medical Center. Self-report questionnaires were used in this study. Purposive samplings were chosen to recruit respondents in Hualien, Taiwan. The valid data for this study were provided by 445 medical volunteers including 160 males and 285 females. Linear regression analysis and Fisher's Z Transformation were used to testify the moderation of gender on the relationship between social capital and well-being. The results indicated that medical volunteers' social capital was positively associated with their general well-being. Although there were positive effects of social capital on four dimensions of well-being (life satisfaction, interpersonal relationship, self-affirmation and physical-mental health), there was no significant gender differences was found. In general, the results of this study provided direct evidences to support theories of social capital, need-hierarchy and symbolic interaction in the context of medical volunteering. Finally, the theoretical and practical implications of the findings were discussed.