Ce0.8Sm0.2O2-delta, Ce0.8Nd0.2O2-delta and Ce0.8Sm0.1Nd0.1O2-delta samples were prepared by a citrate sol-gel method. Effects of microstructures and oxygen vacancies of the samples on their electrical properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), in situ Raman spectroscopy and AC impedance spectroscopy. SEM results indicated that larger grains were formed on the Ce0.8Nd0.2O2-delta and Ce0.8Sm0.1Nd0.1O2-delta electrolytes compared to that on the Ce0.8Sm0.2O2-delta. In situ Raman spectra suggested that the concentration of oxygen vacancies of the Ce0.8Sm0.1Nd0.1O2-delta sample was the highest while that of Ce0.8Sm0.2O2-delta was the lowest. It was found that the difference in the electrical, conductivity for these electrolytes was closely related to the microstructure and oxygen vacancies of the samples. The highest electrical conductivity obtained on the Ce0.8Sm0.1Nd0.1O2-delta sample was ascribed to its larger grain size and higher concentration of oxygen vacancies. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.