Ceria-based solid electrolytes are reviewed in terms of electrical conductivity, diffusivity and transference number. The electrical conductivity and diffusion constants of various fluorite compounds are compared and those of ceria-based oxides are almost the highest among these fluorite oxides. The electrical conductivity of doped ceria is much dependent on the kind and the concentration of dopants. The reason for this behavior and a guideline to obtain more electrically conductive materials are discussed. The effect of sample preparation on the electrical conductivity is described in terms of the character of raw materials, impurities and the sintering condition. The factors to determine the transference number and the methods to increase the transference number at low oxygen pressures are also discussed.