Abstract Chemodynamic therapy (CDT) is a novel tumor treatment method by using hydroxyl radicals ( • OH) to kill cancer cells. However, its therapeutic effects are strictly confined by the short lifespan of • OH and reduced • OH generation speed. Herein, an effective CDT is achieved by both improving • OH lifetime and long‐lasting generating • OH through intraparticle electron transfer within heterogeneous nanoparticles (NPs). These heterogeneous NPs are composed of evenly distributed Cu and Fe 3 O 4 (CFO NPs) with large interaction interfaces, and electrons tend to transfer from Cu to Fe 3 O 4 for the appearance of ≡Cu 2+ and increase in ≡Fe 2+ . The generated ≡Cu 2+ can interact with GSH, which prolongs the lifespan of • OH, produces ≡Cu + for higher speed • OH generation with H 2 O 2 , and induces cell ferroptosis for tumor therapy. The improved ≡Fe 2+ can also improve the • OH release under H 2 O 2 until Cu is depleted. As a result, a sustainable • OH generation is achieved to promote cell apoptosis for effective tumor therapy. Since H 2 O 2 and GSH are only overexpressed at tumor, and CFO NPs can degrade in the tumor microenvironment, these NPs are with high biosafety and can be metabolized by urine. This work provides a novel biomaterial for effective cancer CDT through intraparticle electron transfer.