The BaCo 0.7 Fe 0.3− y Nb y O 3− δ oxides (BCFNy, y=0.00–0.12) were synthesized by the conventional solid state reaction process and investigated as a novel cathode for intermediate temperature solid oxide fuel cells(IT-SOFCs). Cubic perovskite, with enhanced phase stability at higher Nb concentration, was obtained at y⩾0.04. The unit cell volumes increased with y, reached a maximum at y=0.10, and then decreased. The niobium doping concentration also had a significant effect on the electrochemical performance of BCFNy materials. Among the various BCFNy oxides tested, BCFN0.10 possessed the smallest interfacial polarization resistance (R p ). The R p was as low as 0.9406, 0.1300, 0.0211, and 0.0082Ωcm 2 at 500, 600, 700, and 800°C, respectively. With a 220μm-thick Sm 0.2 Ce 0.1 O 1.9 (SDC) as electrolyte and BCFN0.10 as the cathode, a fuel cell provides maximum power densities of 202, 350, 569, 820, and 1006mWcm −2 at 600, 650, 700, 750, and 800°C, respectively. The encouraging results suggested that BCFN0.10 was a very promising cathode material for IT-SOFCs.