Indoped ZnO thin films were prepared on glass substrate by RF magnetron sputtering. The result of XRD and AFM shows that the films are polycrystalline with high caxis orientation. The study of gas sensing reveals that the films are sensitive to NO2 and the best sensibility occurs at 273 ℃; the sensibility is concerned with the concentration of NO2 and the film thickness. The ZnO∶In films are more sensitive to the NO2 gas with higher concentration of NO2 and thinner films have a better sensitivity. Exposed to 2×10-5 NO2 at 273 ℃, the 90nm thick film has a sensibility of 16, indicating that ZnO∶In films can be used to measure NO2 with a low concentration.