AbstractIn acidic proton exchange membrane water electrolysis (PEMWE), the anode oxygen evolution reaction (OER) catalysts rely heavily on the expensive and scarce iridium‐based materials. Ruthenium dioxide (RuO₂) with lower price and higher OER activity, has been explored for the similar task, but has been restricted by the poor stability. Herein, we developed an anion modification strategy to improve the OER performance of RuO₂ in acidic media. The designed multicomponent catalyst based on sulfate anchored on RuO₂/MoO₃ displays a low overpotential of 190 mV at 10 mA cm⁻² and stably operates for 500 hours with a very low degradation rate of 20 μV h⁻¹ in acidic electrolyte. When assembled in a PEMWE cell, this catalyst as an anode shows an excellent stability at 500 mA cm⁻² for 150 h. Experimental and theoretical results revealed that MoO₃ could stabilize sulfate anion on RuO₂ surface to suppress its leaching during OER. Such MoO₃‐anchored sulfate not only reduces the formation energy of *OOH intermediate on RuO₂, but also impedes both the surface Ru and lattice oxygen loss, thereby achieving the high OER activity and exceptional durability.