The main aim of this study was to examine one potential mediator of the prospective association between depressive symptoms and peer victimization: sadness rumination. Data were collected from 302 early adolescents (M[subscript age] = 10.53, SD =0.16; 55.3% girls), at two waves, 1-year spaced, using self-reports. Depressive symptoms preceded increases in peer victimization and sadness rumination. Sadness rumination preceded increases in peer victimization. Sadness rumination mediated the relationship between depressive symptoms and increases in peer victimization. Multi-group analysis indicated that the mediation model tested was significant for boys, but not for girls. Overall, depression-related peer victimization could be minimized with intervention programs targeting early adolescents' sadness rumination tendencies. Future research should further explain why depressed boys may face greater risk than girls in displaying increases in sadness rumination over time, which in turn, may lead to more frequent experiences of peer victimization.