The effects of UV light illumination on the gas sensing performances of zinic oxide-tin oxide (ZnO-SnO₂) thick film sensor toward ethanol have been investigated. The nanopowder sizes of SnO₂synthesized by precipitation process are about 30 nanometer. The commercial ZnO powder in various weight ratios (10 similar to 90 wt%) were mixed into SnO₂nanopowder. The results of gas properties measurement show that there is obvious enhancement in the sensitivity to ethanol with UV light illumination. As be exposed to 100 ppm ethanol, the sensor based on 30 wt% ZnO-70 wt% SnO₂mixed sensitivity materials has a sensitivity of up to 10 with UV light illumination. The X-ray diffraction (XRD) characterization reveals that the sensitive materials are the mixture of SnO₂with ZnO and without anything else. The reason for that the gas sensitivity of the mixture of ZnO and SnO₂was increased is presumably that the ZnO enhances the ability to transfer photo-generated charge and then increases the sensitivity under UV illumination.