This chapter examines the relationship between social media use and subjective well-being (SWB) among older adults in China, using data from the 2020 China Longitudinal Aging Social Survey (CLASS). Focusing on three SWB indicators in terms of life satisfaction, loneliness, and feelings of uselessness, the study finds that social media users generally report better well-being than non-users. While the positive association with life satisfaction diminishes after controlling for confounders, the relationships with reduced loneliness and uselessness remain significant, particularly among vulnerable subgroups such as rural residents, those with disabilities, and individuals with higher education. Purpose-specific analyses reveal that using social media for health management and information seeking is linked to enhanced SWB, while usage for shopping or travel correlates with increased loneliness. These findings underscore the importance of meaningful and goal-oriented digital engagement in promoting well-being. The study highlights the need for inclusive digital literacy programs and health-integrated platform design to support healthy aging in a rapidly digitalizing society.