In2O3-ZnO composite thin films were fabricated and their NOx sensing characteristics were investigated in this study. The content of ZnO in In2O3-ZnO thin film was controlled by adjusting the Zn2+/In3+ molar ratio (r) during the film preparation. The results showed that the incorporation of ZnO into the In 2O3 thin film can greatly improve the sensor reponse to NOx at operation temperature below 200 oC. However, as the ZnO content was further increased, the grain of the composite film started to merge into big ones, and thus decreased the surface area, resulting in lower sensor responses. The detection limit (S/N=3) of In2O3-ZnO composite film (r=0.67) reached 12 ppb at 150 °C. Both pure In2O3 and In2O3-ZnO composit films (r=0.67) showed no response to CO gas.