A series of fluorite samples with the Ce0.8La0.2-xTlxO2-delta (TxLDC, x = 0-0.09) composition were prepared via a simple polyol process. Samples were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) attached with an energy dispersive X-ray spectroscopy (EDXS) system, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Pycnometer and impedance spectroscopy. Dense ceramics were prepared by sintering the pellets at 1400 degrees C for 7 h. The results show that the Tl content (x) affects the properties of Ce0.8La0.2-xTlxO2-delta. The fluorite with x = 0.07 is suggested as the most promising composition for a solid oxide fuel cell electrolyte material since it has shown to have a high electrical conductivity (3 x 10(-2) Scm(-1) at 650 degrees C) and a low activation energy (0.69 eV). The ionic conductivity is almost stable at functional temperature (550 degrees C) for an extended period of time. It is therefore concluded that co-doping with the appropriate amount of Tl has a great potential to become a new important electrolyte for commercial IT-SOFCs. Copyright (c) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.