Civil society emphasizes the importance for citizens to be involved and developed in association with other people. The importance of socialization for citizens to learn civic values and develop virtues of tolerance and solidarity is generated by voluntary associations. Mediating structures are the entities that help to integrate disconnected elements of civil society and strengthen communities. Social capital is one of the elements that is actively utilized by mediating structures to connect people to, and get involved with others in mobilizing their efforts collectively for both public and private causes through volunteering. Traditionally only charitable nonprofits were perceived to be mediating structures. However, there are scattered examples of non-charitable professional membership 501(c)(6) associations engaging themselves and their members in social programs and community volunteering unaccountable for in the literature. Using the theories of mediating structures and social capital this research questions the assumption of limited applicability of mediating structures. Extensive empirical analysis of the American Society of Association Executives (ASAE) dataset is performed to determine how social capital and other organizational factors affect the performance of mediating roles by professional membership associations.