Sirt6, a class III NAD⁺-dependent deacetylase of the sirtuin family, is a highly specific H3 deacetylase and plays important roles in regulating cellular growth and death. The induction of oxidative stress and death is the critical mechanism involved in cardiomyocyte injury and cardiac dysfunction in doxorubicin-induced cardiotoxicity, but the regulatory role of Sirt6 in the fate of DOX-impaired cardiomyocytes is poorly understood. In the present study, we exposed Sirt6 heterozygous (Sirt6^+/-) mice and their littermates as well as cultured neonatal rat cardiomyocytes to DOX, then investigated the role of Sirt6 in mitigating oxidative stress and cardiac injury in the DOX-treated myocardium. Sirt6 partial knockout or silencing worsened cardiac damage, remodeling, and oxidative stress injury in mice or cultured cardiomyocytes with DOX challenge. Cardiomyocytes infected with adenoviral constructs encoding Sirt6 showed reversal of this DOX-induced damage. Intriguingly, Sirt6 reduced oxidative stress injury by upregulating endogenous antioxidant levels, interacted with oxidative stress-stirred p53, and acted as a co-repressor of p53 in nuclei. Sirt6 was recruited by p53 to the promoter regions of the target genes Fas and FasL and further suppressed p53 transcription activity by reducing histone acetylation. Sirt6 inhibited Fas/FasL signaling and attenuated both Fas-FADD-caspase-8 apoptotic and Fas-RIP3 necrotic pathways. These results indicate that Sirt6 protects the heart against DOX-induced cardiotoxicity by upregulating endogenous antioxidants, as well as suppressing oxidative stress and cell death signaling pathways dependent on ROS-stirred p53 transcriptional activation, thus reducing Fas-FasL-mediated apoptosis and necrosis. •Sirt6 is significantly decreased in DOX-insulted mouse hearts and cardiomyocytes. •Sirt6 attenuates DOX-induced cardiac atrophy, dysfunction and oxidative stress. • Sirt6 reduces oxidative stress injury by upregulating endogenous antioxidants. • Sirt6 interacts with p53 as a co-repressor to suppress p53 transcriptional regulation and inhibits Fas-FasL-mediated apoptosis and necrosis downstream of p53.