AbstractThe development of efficiently active and stable bifunctional noble‐metal‐based electrocatalysts toward overall water splitting is urgent and challenging. In this work, a rutile‐structured ruthenium‐zinc solid solution oxide with oxygen vacancies (Ru_0.85Zn_0.15O_2‐δ) is developed by a simple molten salt method. With naturally abundant edges of ultrasmall nanoparticles clusters, Ru_0.85Zn_0.15O_2‐δ requires ultralow overpotentials, 190 mV for acidic oxygen evolution reaction (OER) and 14 mV for alkaline hydrogen evolution reaction (HER), to reach 10 mA cm⁻². Moreover, it shows superior activity and durability for overall water splitting in different electrolytes. Experimental characterizations and density functional theory calculations indicate that the incorporation of Zn and oxygen vacancies can optimize the electronic structure of RuO₂ by charge redistribution, which dramatically suppresses the generation of soluble Ru^x>4 and allows optimized adsorption energies of oxygen intermediates for OER. Meanwhile, the incorporation of Zn can distort local structure to activate the dangling O atoms on the distorted Ru_0.85Zn_0.15O_2‐δ as proton acceptors, which firmly bonds the H atom in H₂O* to stabilize the H₂O and considerably improves the HER activity.