Three different ZnO nanostructures (nanorods/flowers/spheres) were prepared through facile hydrothermal method or water bath, whose sensing properties to NO₂were investigated in detail at room temperature acti-vated by UV light (365 nm LED). The sensing results showed that ZnO nanospheres exhibit the highest response of 29.4–5 ppm NO₂, which can be attributed to their biggest specific surface area and the most amount of adsorbed oxygen species on the surface. In contrast, ZnO nanorods show the fastest response and recovery speed (9 and 18 s to 5 ppm NO₂, respectively) due to their highest crystallinity, least surface defects and unidirectional electron transfer path, which is much faster than most reported literatures. With regard to the ZnO nanoflowers, both the gas-sensing response and the response and recovery speed are between ZnO nanorods and ZnO nano-spheres. Furthermore, the stability, selectivity, and the moisture resistance of three different ZnO nanostructures were also researched.