Social shopping communities, representing a special form of social media, have offered fertile ground for members to communicate their opinions and exchange product information. The goal of our paper is to understand this new business model of social shopping communities and investigate why members voluntarily share information on social shopping communities. We integrate theories of collective action and social capital theory to construct a research model for investigating the motivations behind members' posting behavior. By analyzing panel data collected from a social shopping community, we found that members posting behavior is determined by reputation, enjoyment of helping, network centrality, member expertise, as well as reciprocity. The results of this study provide important implications for both research and practice.