Studying abroad entails international students' identity (trans)formation and social network development, but individuals' decisions and choices while engaging in these processes remain underexplored. Informed by the notion of agency in second language socialization theory, this longitudinal case study examined the interplay of identity and social network in the socialization experiences of three international students learning Chinese as an additional language in China. Analysis of ethnographic interviews, a Study Abroad Network Questionnaire, observational field notes, and supplementary data revealed the role of individual agency in mediating the students' heterogeneous ways of mobilizing linguistic and cultural resources to construct identities and build social ties. The study also illustrated that agency was not readily or equally accessible to all participants, but it was negotiated in the nexus of their identity and social network. Finally, the study discussed the issues that surfaced in students' distinctive learning trajectories, and offered implications to inform potential stakeholders.