In this study, we adopt social capital theory to explore the factors that drive PTT Anti-Cancer Board members to provide online social support. We surveyed 150 members to test and validate the model and relationships. The results show that while relational and structural dimension of social capital can boost community members to provide both action-facilitating and nurturant style social support, cognitive dimension of social capital can only drive members to offer action-facilitating style social support. Discussions and implications of the findings are also provided.