Nowadays, gas sensors with high response and short response/recovery time at room temperature (RT) are of great interest to researchers. This work demonstrated a gas sensor based on the composites of CsPbBr₃quantum dots (QDs) and ZnO microballs (MBs) for NO₂detection at room temperature. Compared with pure ZnO MBs, the composites decorated with 1.0 wt% QDs showed the optimal sensitivity under the 520 nm light activation. The response of 1.0 wt% QDs-ZnO sensor to 5 ppm NO₂was about 53, and the response/recovery time were about 63 s and 40 s, respectively. The sensor also showed good repeatability during six cycles and superior selectivity than other gases such as CO, NH₃, and acetone. The addition of QDs can realize the absorption of visible light by the sensor and improve the utilization of light energy. Under the light excitation, the conductivity of the composites is significantly increased and the activity of oxygen species on the surface is also improved, which is conducive to the adsorption/desorption of gas molecules.