ABSTRACT The COVID-19 pandemic caused widespread disruption as governments took actions to limit the spread of the virus. Measures such as physical distancing and lockdowns changed living conditions, leading to challenges such as social isolation and reduced connectedness. This study explores COVID-19’s impact on adolescents’ well-being, emphasising family social capital, which refers to supportive adult-child relationships that foster well-being and enhance remote learning. Quantitative data was collected through an online survey from August 2022 to August 2023, involving 4008 students and 3511 parents. Semi-structured interviews with six students and their parents (either the mother or the father) provided in-depth insights into the perceived role of family social capital in shaping adolescents’ well-being during quarantine. Quantitative data revealed that parental education level significantly influenced adolescents’ self-reported well-being and resilience, and family income influenced parents’ perceptions of their children’s well-being. Qualitative data highlighted the importance of strong family bonds, effective parent-child relationships, and robust family support in mitigating the adverse effects of prolonged home quarantine. The research also discovered the role of adolescents’ agency in building social capital through web-based communities. The study contributes to understanding Chinese adolescents’ well-being during the COVID-19 pandemic, providing implications for supporting their well-being in the post-pandemic era.