Use of social network sites (SNSs) has been shown to lead to social capital, connections people can rely on for support. Most previous research has focused on the case in which people participate in only one SNS (usually Facebook). However, for some people, legal, linguistic, cultural and other barriers make it impossible to interact with all friends and acquaintances on a single site. For example, Chinese international students in the U.S. often use Facebook to connect with American peers but Renren their friends back home. This dissertation explores the effects of this dual SNS use on social capital development. Specifically, I address four research questions: a) How do the awareness of relational benefits and motivation to have casual and close friends affect relational maintenance and communication with different sub-networks on Facebook/Renren? b) How do relational maintenance and communication with different networks lead to psychological investment in Facebook/Renren? c) What forms of social capital are developed on Facebook/Renren? d) How do forms of social capital on Facebook/Renren contribute to the participants' sociocultural adaptation in the U.S.? I conducted a survey of 287 Chinese international students in the U.S. and used structural equation modeling to analyze the relationships among key constructs. The results show that a) the awareness of relational benefits of casual friends significantly relates to relational maintenance and i communication with friends on Facebook/Renren but the motivations yield mixed results; b) relational maintenance and communication with different networks are significantly related to psychological investment in Facebook/Renren, but not communication with Americans; c) psychological investment significantly contributes to bonding and bridging social capital, but not bonding social capital on Facebook; d) bonding and bridging social capital significantly contribute to the participants' adaptation, but not bridging social capital on Facebook. This work contributes to theories of SNS use by showing that awareness and motivation are two important indicators to study in terms of social capital development and by providing evidence that Chinese users acquire different forms of social capital through networks on different SNSs. It also introduces a new scale for measuring bridging social capital scale that ties more closely to the literature. ii