The structure, thermal expansion coefficients and ionic and electronic conductivities of Ce1-xBixO2-delta (x = 0-0.30) solid solutions prepared hydrothermally were investigated. The uniformly small particle size (25-50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 900-1300 degrees C, a significantly lower temperature, compared to that at 1600-1650 degrees C required for ceria solid electrolytes prepared by solid state techniques. The solubility limit of Bi2O3 in CeO2 was determined to be around 20 mol. %. The maximum conductivity, sigma(600 degrees C) similar to 10(-2) S/cm with E-a = 1.01 eV, was found at x = 0.20. The thermal expansion coefficients, determined from high-temperature X-ray data, are 11.7+/-0.6 X 10(-6) K-1 for CeO2 and, increase with increasing Bi substitution, 16.4 X 10(-6) K-1 at x = 0.20.