The total electrical conductivity, ionic conductivity, and thermopower have been measured as functions of temperature (900 less than or equal to T (degrees C) less than or equal to 1100) and oxygen partial pressure (10(-16) less than or equal to P-o2/atm less than or equal to 1) on the system of Y1-xCaxFeO3 (x = 0.1), a newly proposed solid oxide fuel cell (SOFC) cathode material. The majority ionic carriers are identified as oxygen ions via electrotransport experiments. The ionic conductivity, which is in the range of 10(-4) to 10(-2) S/cm with an activation energy of 1.6 eV in air, tends to increase with increasing P-o2 in oxidizing atmospheres and with decreasing P-o2 in reducing atmospheres. The defect structure of Y1-xCaxFeO3 system is thus explained on the basis of anti-Frenkel disorder. Thermodynamic stability of the system is also discussed.