In this study, the effect of Ga-doping and UV radiation on CO sensing of ZnO nano-powders has been investigated. GZO nanoparticles with different Ga loadings were prepared using a modified sol-gel route and charaterized by means of trasmission electron microscopy (TEM), X-ray diffraction (XRD) and photoluminescence (PL) analysis. Electrical and CO-sensing tests were performed on resistive planar devices consisting of thick films of GZO deposited on interdigitated alumina substrates in both dark and illumination condition by exposing the samples to UV radiation (X = 400 nm). The baseline resistance in dark decreases strongly with the increase of Ga loading. This effect is reinforced by using UV radiation at low temperature in samples containing up to 3 at.% of Ga, which suggests also an effect of the microstructure of GZO on UV light promoting mechanism. The combined effect of Ga doping and UV irradiation allowed to monitor CO in air at low concentration with high sensitivity and lower operating temperature than on unpromoted ZnO sensor. (C) 2015 Elsevier B.V. All rights reserved.