The effect of RE (RE = Ce and Pr) doping LaMnO3 perovskite on crystallographic properties, phase relationships, conductivity, thermal expansion, sintering, and reaction with Y2O3-stabilized ZrO2 electrolyte is presented. La1-xRExMnO3 showed a single perovskite phase in the region 0 less than or equal to x less than or equal to 0.05 for Ce substitution and over the entire composition range of Pr content. No effect of RE doping of LaMnO3 on conductivity was observed. A decrease in thermal expansion coefficients of LaMnO3 accompanied RE doping. Ce doping of LaMnO3 increased its morphological stability and suppressed its reaction with the electrolyte. Ln(1-x)AE(x)MnO(3) (Ln: lanthanum concentration with La, Ce, and Pr, AE = Sr, Ca) materials were examined as cathodes in solid oxide fuel cells. X-ray diffraction analysis indicated that Ln(1-x)AE(x)MnO(3) (0 less than or equal to x less than or equal to 0.3) showed a single perovskite phase. Conductivities of these oxides increased with AE content and ranged from 80 to 200 S/cm at 1000 degrees C in air. and thermal expansion coefficients ranged from 9.5 to 11.6 x 10(-6)/degrees C. Ln(1-x)AE(x)MnO(3) showed less reactivity with the electrolyte compared with La(1-x)AE(x)MnO(3). The cathodic polarization of the (Ln(0.8)Sr(0.2))(0.95)MnO3 at 1000 degrees C was 60 mV at 500 nA/cm(2) in air.