AbstractThe oxygen evolution reaction (OER) suffers from sluggish kinetics even on the benchmark RuO₂ catalyst, due to the complex four sequential proton‐coupled electron transfer steps. Severe electrochemical oxidation and dissolution issues also make RuO₂ fail as an alternative to highly expensive iridium‐based OER catalysts applied in proton exchange membrane water electrolysis. Herein, an acid‐stable W₁₈O_49‐δ matrix‐confined Ru solid solution oxide is developed with considerably reduced Ru loadings beyond commercial RuO₂, to enhance the acidic OER kinetics and extend the long‐term durability simultaneously by incorporating Brønsted acid sites. The representative Ru_0.6W_17.4O_49‐δ with 3D urchin‐like morphology achieves an excellent catalytic stability with ultra‐slow degradation rate and a high mass activity of 27 110 A g⁻¹_Ru @ 1.53 V versus RHE in 0.1 m HClO₄ electrolyte, which is ≈10.8 times higher than that of commercial RuO₂. The enhanced electron transfer from W to Ru during the OER process prevents the over‐oxidation of surface Ru sites extending the long‐term stability, while the incorporated Ru‐O_bri‐W Brønsted acid sites accelerate the deprotonation step by promoting the mobility of proton from the oxo‐intermediate to the neighboring O_bri sites, thus boosting the acidic OER kinetics.