<p>Social support plays a critical role in promoting adolescents’ psychological well-being. However, much of the existing research has relied on cross-sectional data and between-person analyses, limiting our understanding of how social support functions within individuals over time. This limitation is particularly consequential for South Korean multicultural adolescents—a growing and vulnerable population that includes children of international marriages, immigrants, and foreign nationals. Given their increasing numbers and elevated risk for psychosocial challenges, identifying the factors that support their well-being is both a research imperative and a social justice concern. The present study used the random intercept cross-lagged panel models to examine the within-person effects of perceived social support from family, teachers, and peers on South Korean multicultural adolescents’ life satisfaction. This study employed three waves of longitudinal data from a nationally representative sample of South Korean multicultural adolescents (<i>N</i> = 1,635; 48.7% girls; <i>M</i>_age = 9.97 years, SD = 0.37; followed from Grade 4 to Grade 6). Random intercept cross-lagged panel models were employed to disentangle between-person and within-person associations. At the between-person level, higher perceived support from all sources was associated with greater life satisfaction. At the within-person level, only perceived family support positively predicted subsequent life satisfaction, while teacher and peer support did not show significant effects. These findings were consistent across all time points. Overall, the results highlight the unique and dynamic role of family support in shaping multicultural adolescents’ life satisfaction and underscore the importance of distinguishing between different sources and levels of social support in developmental research.</p>