The aim of the present investigation was to study the effect of doping of magnesium and calcium on the ionic conductivity of CeO2 in the system Ce1 - xCax - yMgyO2 - x (x= 0.150) for its use as a solid electrolyte in the intermediate temperature solid oxide fuel cells (IT SOFC).Attempts have been made to synthesize a few compositions in this system with x = 0.150 and y = 0.000, 0.050, 0.060, 0.065 and 0.070. The precursor materials have been synthesized by auto-combustion method. Solid solution forms in compositions with y <= 0.060. Microstructures of thermally etched samples have been studied by scanning electron microscopy (SEM). In order to evaluate the total electrical conductivity, sigma(t), use is made of complex plane impedance analysis. Impedance measurements were made in the frequency range 1 Hz-1 MHz and temperature range 250-500 degrees C. It is found that co-doped samples show higher conductivity than undoped and singly doped samples. (C) 2012 Elsevier B.V. All rights reserved.