In this work, near-completely soft-agglomerated Sm0.2Ce0.8O1.9 powders have been prepared. The pellets were formed and sintered at various sintering conditions of temperature and time. It was found that the sintering conditions have significant effects on the pellet resistivity. By the measurements with the DC four-probe method, it was found that the overall resistivity of the polycrystalline Sm0.2Ce0.8O1.9 material sintered at 1500degreesC increases linearly with the reciprocal of the average grain size. The AC impedance spectroscopy has been used to distinguish the grain resistivity and the apparent grain boundary resistivity. The "brick layer" microstructural model has been used to provide an estimate of the apparent grain boundary resistivity and to relate the electrical properties to the microstructural parameters. By lowering the sintering temperature to 1100-1200degreesC, the true grain boundary resistivity was nearly two orders lower than that sintered at 1500degreesC, and thus the overall resistivity decreases to about 31 ohm-cm at 700degreesC measurement. This makes the Sm0.2Ce0.8O1.9 material capable of working as SOFC's electrolyte at temperatures lower than 700degreesC. (C) 2003 Kluwer Academic Publishers.