This work systematically investigates the effects of single A-site dopant (5 mol% La3+, Sm3+ and Gd3+) and single B-site dopant (5 mol% Zr4+ and Ce4+) on the structure and oxygen reduction reaction of BaFeO3-delta (BFO) used as a cathode for solid oxide fuel cells. The materials are prepared by solid-state method and their structural, electronic, electrocatalytic properties are characterized and compared. Xray diffraction reveals 5 mol% A-site or B-site dopant is sufficient to stabilize the cubic phase of BFO, as predicted by the lattice calculation. X-ray photoelectron spectroscopy and iodometric titration demonstrates that neither of the two doping sites has obvious advantage over the other towards the formation of additional oxygen vacancies. B-site doped BFO shows a lower electrical conductivity than A-site doped ones, however, they have much quicker response to electrical conductivity relaxation, likely originating from the expanded lattice size. With the largest oxygen vacancy concentrations, Ba0.95La0.05FeO3-delta and BaFe0.95La0.05O3-delta stand out from the A-site and B-site doped BFO, respectively, and polarization resistances of 0.029 Omega cm(2) and 0.020 Omega cm(2) are achieved at 700 degrees C, P-O2 = 0.2 atm. With a similar amount of oxygen vacancies, B-site doping is more advantageous for enhancing oxygen bulk diffusion kinetics, and thus ORR activity. (C) 2015 Elsevier B.V. All rights reserved.