Limited empirical research on social capital has investigated the potential downside of social capital on health and well-being. We hypothesized that social capital and mastery might vary according to education with lower-educated persons experiencing fewer advantages. This study used a stratified cluster design to recruit a volunteer sample of 332 adult residents from 7 metropolitan census tracts. The survey included a position generator to collect social capital network data. Generalized estimating equations were used to account for the clustering of respondents in census tracts. Results indicated a differential association between individual social capital and mastery according to educational attainment. Among persons with a high school degree or more, higher social capital was associated with a higher sense of mastery; among less-educated persons, higher individual social capital was associated with lower mastery. Differences in the pathways by which lower- and upper-educated groups access social capital may play a role in social capital's negative association with psychological well-being.