["Aggressive Behavior, Volume 52, Issue 3, May 2026. ", "\nABSTRACT\nWith the growing prevalence of social media use among adolescents, its potential negative consequences warrant serious attention. This longitudinal study examined the associations between three common types of cyber social ostracism, namely cyber personal chat ostracism, cyber group chat ostracism, and cyber personal space ostracism, and adolescent suicidality and bullying behavior, as well as the mediating roles of thwarted belongingness and perceived burdensomeness. A total of 5478 adolescents were assessed across three waves spaced 6 months apart. The results showed that all three forms of online ostracism significantly predicted adolescents' suicidality through elevated thwarted belongingness, and that cyber personal chat ostracism and cyber personal space ostracism further increased suicidality via perceived burdensomeness. Multi‐group analyzes demonstrated that the indirect pathway from cyber personal chat ostracism to suicidality via thwarted belongingness was significantly stronger for girls than for boys, whereas other pathways did not differ by gender. These findings highlight the distinct psychological mechanisms linking online ostracism to self‐directed suicidality in adolescents, and underscore the importance of considering gender differences in prevention and intervention efforts.\n"]