New Sr 0.5 Bi 0.5 FeO 3-δ (SBF) and Sr 0.5 Bi 0.45 FeO 3-δ (SB0.45F) oxides are systematically investigated as oxygen reduction cathodes for intermediate temperature solid oxide fuel cells. The SBF and SB0.45F samples have been discovered that form single-phase solid solutions while maintaining outstanding chemical stability with gadolinium-doped ceria (Gd 0.1 Ce 0.9 O 1.95 , GDC) even sintering at 1000 °C in air. The average thermal expansion coefficients (TECs) for SBF and SB0.45F are very similar to the electrolyte of GDC. XPS and iodometric titration results reveal that A-site deficient SB0.45F cathode possesses a high oxygen vacancy concentration, which can greatly enhance the electro-chemical performance of porous cathode. A low polarization resistance (R p ) is shown for the SB0.45F cathode based on a symmetrical cell test, obtained by electrochemical impedance spectroscopy (EIS). Additionally, the deconvolution results of the EIS test display that the ORR rate of the SB0.45F cathode should be jointly limited by the charge transfer processes and oxygen adsorption processes. The peak power output of a single solid oxide fuel cell (SOFC) equipped with the SB0.45F cathode reaches 0.77 W cm À 2 at 700 °C, about 1.75 times of SBF. These findings suggest that the Bi-deficient SB0.45F perovskite oxide is an outstanding catalyst for IT-SOFC.