It is widely believed that efforts to overcome the collective action problem are more likely to succeed when the level of social capital is high. The analysis in this paper is based on Afrobarometer survey data gathered for Ghana and Nigeria. The statistical analysis explores the variables that influence social capital and political trust. The most important determinant of interpersonal trust in Nigeria and Ghana is trust in political institutions. The findings also suggest that the dimensions of social capital do not form a syndrome as organizational membership has a negative association with interpersonal trust in Nigeria. Thus, the results of this study support the institutional explanation of social capital, while they fail to support Putnam’s civil society explanation. Several demographic variables, such as education, age and ethnicity, also affect social capital and political trust. Contrary to other studies, this study finds a significant negative relationship between education and interpersonal trust.