To develop higher protonic conductivity, we have been studying a new perovskite-type oxide and found that BaPrO3 based perovskite oxides showed high conductivity in a moist H-2 atmosphere. Their conductivity was about 0.1 S/cm at a temperature of 500 degrees C and remained almost constant up to 700 degrees C, which is much higher than that of Ba(Ce0.8Gd0.2)O3-alpha.Ba(Pr1-xGdx)O3-alpha prepared by solid state reaction exhibited an orthorhombic and/or cubic perovskite structure and with a high Gd content was stable in a reducing atmosphere. When Ba(Pr0.7Gd0.3)O3-alpha was used as an electrolyte, the open circuit voltage of the cell was about 1 V and this cell was able to operate at 500 degrees C. During the testing of the cell, the formation of water on an air electrode led us to conclude that mobility of protons in the electrolyte occurred. The dominant conduction species in Ba(Pr1-xGdx)O3-alpha electrolyte were considered as oxygen ions and/or protons.