The potential of neighborhood green spaces to add to community life and promote a better quality of urban living has been recognized. However, it remains unclear which aspects of green space, physical or perceived, best encourage this social capital formation. Particularly in the context of high-density urban environments, the relationship between urban green spaces and social capital remains poorly understood. This study examines their relationship in nine public housing estates in Singapore. The results show that perceived attributes of green space fostered higher levels of social capital than physical attributes. Of the perceptions analyzed, perceived sociability and perceived presence of human activities had the greatest effects on social capital. The findings suggest that physical attributes, such as the amount of green space, matter in shaping perceptions towards green space, which affects, in turn, the level of social capital fostered. In addition, typology of green space contributed to differences in the level of social capital: residents living in estates with distributed green spaces were generally associated with higher levels of social capital than residents living in estates with centralized green spaces. We, therefore, argue that design needs to consider how green spaces are perceived by residents and how they are spatially distributed, over and above the mere presence of green spaces alone.