Oxygen-ion conducting perovskite oxides are important functional materials for solid oxide fuel cells and oxygen-permeable membranes operating at high temperatures (>500 °C). Co-doped perovskites have recently shown their potential to boost oxygen-related kinetics, but challenges remain in understanding the underlying mechanisms. This study unveils the local cation arrangement as a new key factor controlling oxygen kinetics in perovskite oxides. By single- and co-doping Nb5+ and Ta5+ into SrCoO3-δ, dominant factors affecting oxygen kinetics, such as lattice geometry, cobalt states, and oxygen vacancies, which are confirmed by neutron and synchrotron X-ray diffraction as well as high-temperature X-ray absorption spectroscopy, are controlled. The combined experimental and theoretical study unveils that co-doping likely leads to higher cation dispersion at the B-site compared to single-doping. Consequently, a high-entropy configuration enhances oxygen ion migration in the lattice, translating to improved oxygen reduction activity.@en