Nano-scaled tungsten-trioxide (WO3) powder has been synthesized by sot-gel process using tungsten powders. The effect of cerium oxide (CeO2) additive on the gas response of the samples was investigated, especially to the volatile organic compound (VOC) gases, and significant enhancement was achieved. The highest gas response of Ce-added WO3 samples was found to shift to lower temperatures, compared to the pure WO3 ones. The analysis with field-emission SEM reveals that grain boundary is pinned due to adding CeO2, which results in decrease in the average grain size of Ce-added WO3 and increase in the surface area, compared with the pure WO3 ones. Complex impedance spectroscopy analysis indicates that grain boundary resistance increases and grain boundary capacitance decreases with the increasing concentration of CeO2. It means that the Ce ions exist mainly in the WO3 grain boundaries and helps to improve the microstructure. (c) 2007 Published by Elsevier Ltd.