Nd0.20SmxCe0.8-xO1.9-x = 2 (x = 0, 0.05, 0.10, 0.15, 0.20) rare-earth-co-doped ceria electrolytes were synthesized by polyol process. Acetate compounds of cerium and dopants (Nd, Sm) were used as starting materials and triethylene glycol was used as a solvent. Structural and ionic conductivity properties of the electrolyte systems were determined by applying characterization techniques such as X-ray diffraction, the Fourier transform infrared spectroscopy, scanning electron microscope, and electrochemical impedance spectroscopy. The results of X-ray diffraction indicated that a single-phase fluorite structure formed at the relatively low calcination temperature of 600 degrees C. So, the samples were calcined at 600 degrees C for 4 h and then sintered at 1400 degrees C for 6 h to obtain dense ceramics (between 85 and 90%). The two-probe ac impedance spectroscopy was used to study the total ionic conductivity of doped and co-doped ceria samples. The results of the impedance spectroscopy indicate that the Nd0.20Sm0.05Ce0.75O1.875 composition exhibited highest ionic conductivity value, 3.60 x 10(-2) S cm(-1) at 800 degrees C.