Abstract: In this study, the gas sensor properties of ZnO doping with (2 and 4 wt%). Al thin films have been accounted for where the nanocrystalline ZnO based thin films were all around kept by a straight forward and Chemical Spray Pyrolysis (CSP) system. Films have been observed to be uniform, pinhole free and well disciple to the substrate. The morphology, structures and surface harshness of the stored Al doped ZnO thin films were contemplated by different sorts of portrayal strategies. The creators have watched that the sensor reaction and selectivity towards CO gas is enhanced by the Al doping at a low temperature. XRD showed that the acquired films are nanocrystalline in nature with hexagonal wurtzite phase. The films were utilized for identification of CO noticeable all around and most extreme reaction was seen at 175°C. The change in sensor response of ZnO:Al thin films to CO gas credited to the imperfection chemistry, crystallite size and surface" roughness.