The effects of Sr doping on the electrical properties of Ce-0.75(Gd0.95-xSrxCa0.05)(0.25)O2-delta (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05 mol%) electrolytes thick films were investigated. The samples sintered at 1400 degrees C for 8 h. X-ray diffraction (XRD) showed typical XRD patterns of a cubic fluorite structure, and the ionic conductivity was examined by AC impedance spectroscopy. From the experimental results, it was observed that Ce-0.75(Gd0.95-xSrxCa0.05)(0.25)O2-delta (x = 0.04 mol%) electrolytes thick film have higher conductivity and minimum activation energy at 600 degrees C. This is explained in terms of the increased in the oxygen vacancy concentration at the grain boundary. (C) 2013 Elsevier Ltd. All rights reserved.