The structure, thermal expansion coefficients and ionic and electronic conductivities of Ce1-xPrxO2-delta (x = 0-0.50) solid solutions, prepared hydrothermally for the first time, were investigated. The uniformly small particle size (35-50 nm) of the hydrothermally prepared materials allows sintering of the samples into highly dense ceramic pellets at 1300 degrees C, a significantly lower temperature, compared to that at 1600-1650 degrees C required for samples prepared by solid-state techniques. The maximum of total conductivity was found at x = 0.30 (sigma(700 degrees C) = 1.4 x 10(-2) S/cm, sigma(600 degrees C) = 5.9 x 10(-3) S/cm; E-a = 0.47 eV) with electronic contribution to the total conductivity around 50%. The thermal expansion coefficients, determined from high-temperature X-ray data, are 11.8 X 10(-6) K-1 for CeO2 and slowly increase with increasing Pr substitution (12.4 X 10(-6) K- at x = 0.30).