The aim of this research was to investigate the effects of online social networking use on bridging and bonding social relationships as well as on social capital effects. The study examined how the self-systems of users of the social networking website Facebook (where a self-system comprises four elements—self-efficacy, self-assertion, social presence, and self-esteem) and intensity of use affected the abovementioned social relations and social capital effects. Using data from a survey of Facebook users (n =306), the result revealed that Facebook users’ self-systems played an important role in the formation of bridging and bonding social relationships as well as in generating social capital effects. However, self-esteem did not affect bonding social relationships significantly. The study also found that Facebook users’ self-systems mediated the relationship between bridging and bonding social relationships and social capital effects.