Electronic and protonic conductivities of Tb doped SrCeO3 were measured in a hydrogen containing and hydrogen-free atmosphere of the same oxygen partial pressure in 500-900 degrees C. In a H-2 containing atmosphere, the material exhibits mixed electronic and proton-conductivity and, for SrCe0.95Tb0.05O3-delta, the proton transfer number increases with decreasing temperature, from about 0.4 at 900 degrees C to about 0.8 at 500 degrees C. The total conductivity for SrCe0.95Tb0.05O3-delta decreases from about 3 x 10(-3) S/cm in the reducing atmosphere to 4 x 10(-5) S/cm in air at 900 C with an activation energy respectively of 39 kJ/mol and 76 kJ/mol for protonic and n-type electronic conduction. Results of XRD analysis show a decrease in the lattice volume of the SrCe1-xTb O-x(3-delta) With increasing Th concentration. SrCe1-xTb O-x(3-delta) exhibits negligible proton-conductivity with x smaller than 0.005. At 800 degrees C under a reducing atmosphere, SrCe1-xTb O-x(3-delta), with x>0.005, are mixed electronic and proton conductors with a maximum proton-conductivity of about 3 x 10(-3) S/cm at x=0.025 and proton transfer number of about 0.7 for x in the range of 0.005-0.125. (C) 2007 Elsevier B.V. All rights reserved.