Lattice oxygen-mediated mechanism (LOM) on perovskite oxides for oxygen evolution reaction (OER) process has revealed kinetic superiority over conventional adsorbate evolution mechanism (AEM). However, feasibly enhancing the participation of lattice oxygen is still challenging. Here we designed a perovskite cobaltate (La_0.6Sr_0.4Co_0.8Fe_0.1Mn_0.1O_3-δ, LSCFM) nanofiber, and discovered that the co-incorporation of Fe/Mn elements significantly intensifies the involvement of lattice oxygen for OER. Compared with its mono-dopant (Fe or Mn only) counterparts, the LSCFM gives rise to higher surface oxygen vacancies (V_o) concentration and faster oxygen ion diffusion coefficient, endowing a small overpotential of 343 mV at 10 mA cm⁻² and low Tafel slope of 63 mV dec⁻¹. The strongest pH-dependent activity and metal–oxygen covalency are further unveiled on LSCFM by experimental and theoretical approaches, evidencing that the promoted OER kinetics on LSCFM predominantly stems from the formation of reactive lattice oxygen site.