Both social capital and microfinance are central to mainstream development interventions, and both are predicated on the need to recognize the importance of social factors in development. Microfinance institutions mobilize social capital in the form of a group guarantee, and aim to support the development of sustainable financial institutions and income generation. Women are targeted in part because of the effectiveness of their social capital as collateral. However, although social capital is assumed to support development and income generation, the precise dynamics involved in this are rarely explored. This article examines the construction of social capital and its relationship to income generation, based on a long-term ethnographic study of village life in rural Bolivia and the microfinance institution operating there. The author examines the complexity and gendered contradictions implied in the way that social capital is generally viewed to support economic development. It is suggested that the way microfinance institutions use social capital to support sustainable financial institutions and income generation does not always reflect the way that women's networks support access to resources and ultimately, economic development.