The construction of active sites with intrinsic oxygen evolution reaction (OER) is of great significance to overcome the limited efficiency of abundant sustainable energy devices such as fuel cells, rechargeable metal–air batteries, and in water splitting. Anionic regulation of electrocatalysts by modulating the electronic structure of active sites significantly promotes OER performance. To prove the concept, NiFeS electrocatalysts are fabricated with gradual variation of atomic ratio of S:O. With the rise of S content, the overpotential for water oxidation exhibits a volcano plot under anionic regulation. The optimized NiFeS‐2 electrocatalyst under anionic regulation possesses the lowest OER overpotential of 286 mV at 10 mA cm−2 and the fastest kinetics being 56.3 mV dec−1 to date. The anionic regulation methodology not only serves as an effective strategy to construct superb OER electrocatalysts, but also enlightens a new point of view for the in‐depth understanding of electrocatalysis at the electronic and atomic level. Anionic regulation of NiFe (oxy)sulfide electrocatalysts by modulating the electronic structure of oxygen evolution reaction (OER) active sites significantly promotes the water oxidation performance. Antagonistic S/O anions polarize the NiFe active sites, rendering the OER reactivity dependent on the anionic composition. The as‐obtained electrocatalyst exhibits superb OER performance with an ultralow overpotential of 286 mV at an OER current density of 10.0 mA cm−2.