<p>Although the association between adolescents’ sibling relationships and depressive symptoms has been investigated, the within-person bidirectional dynamics between these constructs have remained unclear. Additionally, few studies have examined whether and how sibling structure moderates these associations. To address these gaps, the present study utilized four-wave longitudinal data collected at six-month intervals from 1,927 Chinese adolescents (<i>M</i>_age = 13.67, <i>SD</i>_age = 1.69; 50.06% female). Using a random-intercept cross-lagged panel model, the current study examined the within-person bidirectional dynamics linking sibling warmth, conflict, and rivalry with depressive symptoms, as well as the potential moderating effects of sibling gender composition and age difference. The results revealed significant within-person bidirectional dynamics between sibling conflict and depressive symptoms. In contrast, changes in sibling warmth and rivalry did not predict changes in depressive symptoms, but were instead predicted by them at the within-person level. These associations were not moderated by sibling gender composition or age difference. This study provides empirical evidence for the within-person bidirectional dynamics between sibling relationships and depressive symptoms, highlights the important role of sibling conflict in this process, and suggests that interventions or family education aimed at reducing sibling conflict may help reduce adolescents’ depressive symptoms while also indirectly supporting other dimensions of sibling relationships.</p>