Reactive　oxygen　species　(ROS)-generating　anticancer　agents　can　act　through　two　different　mechanisms:　(i)　elevation　of　endogenous　ROS　production　in　mitochondria,　or　(ii)　formation/delivery　of　exogenous　ROS　within　cells.　However,　there　is　a　lack　of　research　on　the　development　of　ROS-generating　nanosystems　that　combine　endogenous　and　exogenous　ROS　to　enhance　oxidative　stress-mediated　cancer　cell　death.　Methods:　A　ROS-generating　agent　based　on　polymer-modified　zinc　peroxide　nanoparticles　(ZnO2　NPs)　was　presented,　which　simultaneously　delivered　exogenous　H2O2　and　Zn2+　capable　of　amplifying　endogenous　ROS　production　for　synergistic　cancer　therapy.　Results:　After　internalization　into　tumor　cells,　ZnO2　NPs　underwent　decomposition　in　response　to　mild　acidic　pH,　resulting　in　controlled　release　of　H2O2　and　Zn2+.　Intriguingly,　Zn2+　could　increase　the　production　of　mitochondrial　O-2(-)　and　H2O2　by　inhibiting　the　electron　transport　chain,　and　thus　exerted　anticancer　effect　in　a　synergistic　manner　with　the　exogenously　released　H2O2　to　promote　cancer　cell　killing.　Furthermore,　ZnO2　NPs　were　doped　with　manganese　via　cation　exchange,　making　them　an　activatable　magnetic　resonance　imaging　contrast　agent.　Conclusion:　This　study　establishes　a　ZnO2-based　theranostic　nanoplatform　which　achieves　enhanced　oxidative　damage　to　cancer　cells　by　a　two-pronged　approach　of　combining　endogenous　and　exogenous　ROS.