The effect of the Co/Fe ratio was investigated on the crystal structure of perovskite oxides, Pr0.5Sr0.5Co1-xFexO3-δ (x=0, 0.2, 0.5, 0.8, and 1), and on their permeability to oxygen. X-ray diffraction and fluorescence data confirm that continuous solid solutions are formed with the target compositions. All these oxides crystallize as orthorhombic perovskites in the Pnma space group. The lattice parameter increases with the Fe content, while the oxygen permeation flux decreases with the Co/Fe ratio. The oxygen flux is highest through Pr0.5Sr0.5CoO3-δ, with 3.2 × 10-7 mol cm-2 s-1 measured under an air/helium gradient at 900 °C. The activation energy of Pr0.5Sr0.5Co0.5Fe0.5O3-δ is the lowest in this system because its crystal structure is close to that of cubic perovskite.