Based on data from a 2005 survey conducted in Shanghai, China, this research examines the role of social capital in income inequality between rural migrants and urbanites. We find strong income return on social capital, in particular on social capital from strong ties. The paper also observes a great disparity in social capital possession between rural migrants and urban local residents. Although social capital from strong ties seems to be more important for rural migrants than for urbanites, local ties and high-status ties do not seem to benefit rural migrants. Hence, migrants not only suffer severe social capital deficits but also capital return deficits. Given the strong income returns on social capital and the substantial differences in access to and return on social capital between migrants and urban residents, social capital is consequently found to explain a large part of the income inequality between the two groups. Overall, the findings reveal macro-structural effects on the role of social capital in labor market stratification. In China, the lack of formal labor market mechanisms continues to create both a strong need for and opportunities for economic actions to be organized around informal channels via social relations. Yet, the long-standing institutional exclusion of migrants caused by the household registration system has resulted in pervasive social exclusion and discrimination which have substantially limited rural migrants’ accumulation and mobilization of social capital. Under these conditions, social capital reinforces the economic inequality between migrants and urban residents in China. Such empirical evidence adds to understanding the role of social capital in the economic integration of migrants and in shaping intergroup inequality in general.