In this work, we have demonstrated that Cr doping enhances the ethanol sensitivity of ZnO thin film based gas sensor.Cr (0 and 5 wt%) substituted ZnO thin films have been grown on Al2O3 substrate using pre-doped target through RF magnetron sputtering technique. XRD and Raman analyses confirm single phase wurtzite structure of the films and average crystallite size reduces on Cr substitution. SEM images exhibit particles of Cr doped ZnO are more uniform and smaller than the undoped thin film. EDS and XPS spectra revealed successful doping of Cr-(3+) ions and formation of oxygen vacancy on the surface of ZnO film. Moreover, the doping effect enhances the sensitivity of ZnO sensor almost two times and an improvement in the response time/recovery time was also observed. This may be due to increase in surface to volume ratio which leads adsorption of more numbers of ethanol gas molecules at the surface. (c) 2017 Elsevier Ltd. All rights reserved.