A novel gas sensor was fabricated using ZnO nanowalls vertically grown on rGO thin film as sensing materials for detection of NO2 operating at room temperature. The obtained ZnO/rGO hybrids exhibited enhanced performance to 50ppm NO2 (9.61), fast response and recovery behavior (25s, 15s). Display omitted •A gas sensor was fabricated using ZnO nanowalls decorated rGO nanosheets.•The ZnO/rGO hybrids exhibited enhanced performance to 50ppm NO2 (9.61), fast response and recovery behavior (25s,15s).•The mechanism of NO2 gas sensing was discussed. A highly sensitive NO2 gas sensor based on ZnO nanowalls decorated rGO nanosheets was fabricated using a thermal reduction and soft solution process. The highly developed interconnected microporous networks of ZnO nanowalls were anchored homogeneously on the surface of reduced graphene oxide (rGO). Sensors fabricated with heterojunction structures achieved a higher response (S=9.61) and shorter response-recovery (25s, 15s) behavior at room temperature to 50ppm level NO2 effectively in contrast to those sensors based on net ZnO nanowalls or rGO layers. The stability and selectivity of ZnO/rGO heterojunction were carried out. Meanwhile, the effects of humidity on ZnO/rGO heterojunction gas sensor were investigated. The more preferable sensing performance of ZnO/rGO heterojunction to NO2 was discussed. It can be surmised that this NO2 gas sensor has potential for use as a portable room temperature gas sensor.