Nitrogen dioxide (NO₂), as a typical threatening atmospheric pollutant, is hazardous to the environment and human health. Thus, the development of a gas sensor with high response and low detection limit for NO₂detection is highly important. The highly ordered mesoporous indium trioxide (In₂O₃) prepared by simple nanocasting method using mesoporous silica as template and decorated with Au nanoparticles was investigated for NO₂detection. The prepared materials were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. Characterization results showed that the samples exhibited ordered mesostructure and were successfully decorated with Au. The gas sensing performance of the sensors based on a series of Au-loaded mesoporous In₂O₃were systematically investigated. The Au loading level strongly affected the sensing performance toward NO₂. The optimal sensor, which was based on 0.5 wt% Au-loaded In₂O₃, displayed high sensor response and low detection limit of 10 ppb at low operating temperature of 65℃. The excellent sensing properties were mainly attributed to the ordered mesoporous structure and the catalytic performance of Au. We believe that the Au-loaded mesoporous In₂O₃can provide a promising platform for NO₂gas sensors with excellent performance.