The exploration of high-efficiency and Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) remains a tremendous challenge. Herein, an ultrafine FeNi–Mo₂C composite immobilized on the surface of SiO₂ support is fabricated through annealing a mixture of Fe, Ni and Mo precursors and SiO₂ nanospheres. The electronic structure of the FeNi alloy is tuned by combining with Mo₂C, forming a hybrid architecture with enhanced intrinsic activity of active sites. The introduced SiO₂ nanospheres reduce the nanoparticle size of the FeNi–Mo₂C composite, further increasing the population of the surface electrochemically active sites. Benefiting from the compositional and structural merits, the FeNi-Mo₂C@SiO₂ electrocatalyst exhibits excellent OER behavior with a small overpotential of 180 mV to reach a current density of 10 mA cm⁻², an ultra-small Tafel slope of 11.0 mV dec⁻¹, and good stability in alkaline media. The outstanding OER performance is attributed to the increased number and enhanced intrinsic activity of active sites due to the synergistic effect of each component. This study provides a promising way to design and develop an advanced electrocatalyst towards water oxidation.