Al-ZnO/CuO nanocomposite based gas sensor exhibits high sensitivity, good selectivity, fast response and recovery time to ammonia at R.T. Display omitted •Low cost sol–gel synthesis of pure ZnO, ZnO/CuO and Al-ZnO/CuO nanocomposites.•Oxygen active sites are increased by forming porous structured films.•High selectivity towards ammonia even at low concentration.•The sensor has good repeatability, fast response and recovery time towards ammonia. Pure ZnO nanoparticles (NPs), ZnO/CuO and Al-ZnO/CuO nanocomposites (NCs) were prepared using co-precipitation followed by sol–gel method. The structural and morphological properties of resulting materials were characterized by X-ray diffraction (XRD), micro Raman, high-resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM) respectively. The XRD results confirmed that the ZnO-CuO composite is formed without the presence of any ZnO-CuO alloy. The gas sensing performance of pure ZnO, ZnO/CuO and Al-ZnO/CuO nanocomposites towards ammonia gas at room temperature was investigated. The gas sensing results revealed that the Al-ZnO/CuO nanocomposite based gas sensor has superior gas sensing properties like, high response, good stability, and fast response (14s) and recovery (9 s) time towards 500ppm (parts per million) ammonia gas at room temperature compared to pure ZnO and ZnO/CuO based sensors. Further the gas sensing performance of Al-ZnO/CuO sensor towards different volatile organic compound (VOC) gases was tested.