Given the widespread use of social networking sites across the world and their importance in people’s lives, explaining users’ well-being on these platforms is certainly worthy of research inquiry. However, little attention has been given to well-being in the context of social networks. Building on the dual process model of the self-determination theory, we hypothesized that for the relatedness need, 1 of 3 basic psychological needs, its satisfaction (RNS) and frustration (RNF) might trigger different motivations (autonomous vs. controlled) and in turn affect people’s social networking well-being. Data were collected through self-reported questionnaires from 494 freshmen (Mage = 18.81 ± 0.92 years, 190 men). Structural equation modeling analyses supported the hypothesized model: Autonomous and controlled motivations partially mediated the relationship between RNS or RNF and social networking well-being. Specifically, RNS was significantly related to positive affect in social networks, being mediated by autonomous motivation. RNF was significantly related to negative affect and general well-being in social networks, with the former relation being mediated by controlled motivation. It can be concluded that RNS and RNF play pivotal but distinct roles in shaping individuals’ motivation and further exert an important influence on the level of well- or ill-being during social networking usage. Implications for future research are discussed.