Nanocrystalline Sm3+ and Nd3+ co-doped CeO2 thin-film electrolytes with high in-plane electric conductivities have been deposited via radio frequency magnetron sputtering. The results show that with increased RF power or decreased pressure, a reduction in the level of porosity of the film takes place, along with an increased electric conductivity. Maximum electric conductivity of 9 x 10(-3) S cm(-1) at 500 degrees C was achieved with optimal sputtering process. It also indicates that with the change of the substrate from single crystal alumina to polycrystalline alumina, the film structure varies from (111) preferred orientation to random orientation, accompanied by an enhancement in electric conductivity. Compared with alumina substrates, the quartz substrate shows a negative effect on electric conductivity. (C) 2011 Elsevier Ltd. All rights reserved.