The structure, thermal expansion and ionic conductivity of solid electrolytes based on samarium doped cerium oxide, Ce1-xSmxO2-x/2 (x = 0-0.30), prepared by the sol-gel method were systematically investigated in a wide range of temperature of 200-650 degrees C. The uniformly small particle size of the sol-gel prepared materials allows sintering of the samples into highly dense ceramic pellets at significantly lower temperature 1400 degrees C compared to that of 1600 degrees C required for samples prepared by solid state techniques. The ionic conductivity increases with increasing samarium substitution and reaches a maximum for the composition Ce0.80Sm0.20O1.9 (similar to 5 x 10(-3) S cm(-1) at 600 degrees C). Thermal expansion coefficients range between 8-10 x 10(-6) K-1.