This study explores the impact of Social Network Sites (SNSs) usage on the formation of online bridging and bonding social capital, and the relationship between online and offline social capital. It is hypothesized that use of SNSs forms online social capital and online and offline social capital are positively correlated. A Chinese SNS, Renren, is studied specifically. Social capital scales and personality measures were adapted from existing literature to develop a questionnaire and a survey of 183 students was conducted in a university in China. Regression analyses suggest a strong positive relation between use of SNSs and online bridging social capital. Online social capital is demonstrated to be positively correlated with offline social capital. User extraversion is shown to predict certain use behaviors but its interaction effect with SNSs usage is not significant. Discussions about the theoretical and practical implications of the findings are provided.