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Abstract Using both density functional theory (DFT+U) simulations and experiments, we show that the incorporation of an ordered array of oxygen‐vacancies in a perovskite oxide can lead to enhancement of the electrocatalytic activity for the oxygen‐evolution reaction (OER). As a benchmark, LaCoO₃was investigated, where the incorporation of oxygen‐vacancies led to La₃Co₃O₈(LaCoO_2.67), featuring a structural transformation. DFT+U simulations demonstrated the effect of oxygen‐vacancies on lowering the potential required to achieve negative Gibbs Free Energy for all steps of the OER mechanism. This was also confirmed by experiments, where the vacancy‐ordered catalyst La₃Co₃O₈(LaCoO_2.67) showed a remarkable enhancement of electrocatalytic properties over the parent compound LaCoO₃that lacked vacancies. We also synthesized and studied an intermediate system, with a smaller degree of oxygen‐vacancies, which showed intermediate electrocatalytic activity, lower than La₃Co₃O₈and higher than LaCoO₃, confirming the expected trend and the impact of oxygen‐vacancies. Furthermore, we employed additional DFT+U calculations to simulate a hypothetical material with the same formula as La₃Co₃O₈but without the vacancy‐order. We found that the gap between centers of Codand Opbands, which is considered an OER descriptor, would be significantly greater for a hypothetical disordered material compared to an ordered system.