In this study, the ceramic powders of Ce1-xGdxO2-x/2 and Ce1-xNdxO2-x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were synthesized by ultrasound assisted co-precipitation method. The ionic conductivity was studied as a function of dopant concentration over the temperature range of 300-800 degrees C in air, using the impedance spectroscopy. The maximum ionic conductivity, sigma(800 degrees C)=4.01 x 10(-2) Scm(-1) with the activation energy, E-a=0.828 kJmol(-1) and sigma(800 degrees C)=3.80 x 10(-2) Scm(-1) with the activation energy, E-a=0.838 kJmol(-1) were obtained for Ce0.90Gd0.10O1.95 and Ce0.85Nd0.15O1.925 electrolytes, respectively. The average grain size was found to be in the range of 0.3-0.6 mu m for gadolinium doped ceria and 0.2-0.4 mu m for neodymium doped ceria. The uniformly fine crystallite sizes (average 12-13 nm) of the ultrasound assisted prepared powders enabled sintering of the samples into highly dense (over 95%) ceramic pellets at 1200 degrees C (5 degrees C min(-1)) for 6h. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.