Ceria co-doped with Sm 3+ and Nd 3+ powders are successfully synthesized by citric acid-nitrate low-temperature combustion process. In order to optimize the electrical properties of the series of ceria co-doped with Sm 3+ and Nd 3+, the effects of co-doping, doping content and sintering conditions on grain and grain boundary conductivity are investigated in detail. For the series of Ce 0.9(Sm xNd 1- x) 0.1O 1.95 (x = 0, 0.5, 1) and Ce 1- x(Sm 0.5Nd 0.5) xO δ (x = 0.05, 0.10, 0.15, 0.20) sintered under the same condition, Ce 0.9(Sm 0.5Nd 0.5) 0.1O 1.95 exhibits both higher grain and grain boundary conductivity. Compared with Ce 0.9Gd 0.1O 1.95 and Ce 0.8Sm 0.2O 1.9, Ce 0.9(Sm 0.5Nd 0.5) 0.1O 1.95 sintered at 1350-1400 °C shows higher total conductivity with the value of 1.0 × 10 -2 S cm -1 at 550 °C. In addition, it can be found the trends of grain and grain boundary activation energies of Ce 1- x(Sm 0.5Nd 0.5) xO δ are both consistent with those of Ce 1- xNd xO δ, but different from those of Ce 1- xSm xO δ, which can be explained as: the local ordering of oxygen vacancies maybe occurs more easily in Nd-doped ceria than in Sm-doped ceria; the segregation amount of Sm 3+ is more than that of Nd 3+ to the grain boundaries in ceria co-doped with Sm 3+ and Nd 3+, which is confirmed by X-ray photoelectron spectroscopy (XPS).