Crystal structure, microstructure, electrical conductivity, and electrochemical performance of a family of iron perovskites with the general formula Ln0.5M0.5FeO3-δ (Ln=La and Pr; M=Sr, Ca, and Ba) has been studied as functions of mean A cation radius 〈rA〉. All the samples have a rhombohedral structure (space group: R ̄3c). Scanning electron microscope images show that the average grain size decreases with increasing 〈rA〉. The dc four-probe measurements indicate that all samples have high electrical conductivity, increasing with 〈rA〉. The electrochemical behavior of these cathode materials was evaluated by using current-voltage curve measurements and ac impedance spectroscopy over three-electrode electrolyte supported cells. The results show an improvement in cathode performance and a significant decrease in polarization resistance with increasing mean A cation radius 〈 rA 〉. © 2010 The Electrochemical Society.