This study examined whether and how the usage of social media can influence college students' level of network heterogeneity and how network heterogeneity is associated with levels of bridging/bonding social capital and subjective well-being. In particular, whether network heterogeneity plays a mediating role in the relationship between social media use and the dependent variables of bridging/bonding social capital and subjective well-being was investigated. The results indicated that usage of social media is positively associated with college students’ communication network heterogeneity in their everyday life. Network heterogeneity is also positively related to levels of bridging/bonding social capital and subjective well-being. We also discovered a positive indirect effect mechanism by which social media use influences bridging/bonding social capital and subjective well-being through network heterogeneity. •Social media use increases network heterogeneity.•Network heterogeneity positively influences social capital and subjective well-being.•The heterogeneity mediates the relationship between social capital and well-being.