According to recent reports, the most of semiconductor gas sensors had the higher operating temperature (from 100 to 300 degrees C), which caused the decrement of selectivity and restricted its application. In this study, we prepared the ordered porous Cr2O3/ZnO (OP-Cr2O3/ZnO) gas sensor materials with p-n heterojunction structure, successfully. Firstly, we synthesized ordered porous zinc oxide matrix by soft template method, and then the surface of the ZnO matrix was modified by silane coupling agent to increase the activity of surface. The Cr2O3 film was assembled to the surface of the modified matrix through ultrasonic chemical plating method, and the ordered porous Cr2O3/ZnO composite material was obtained. The prepared ordered porous Cr2O3/ZnO gas sensor showed excellent response and selectivity toward NO,, gas at room temperature (25 degrees C +/- 2 degrees C). When the NO,, concentration was 100 ppm, the response could reach to 86.7% and the response time was only 4 s, the detection limit was only 0.05 ppm. The superior gas sensing properties of the OP-Cr2O3/ZnO could been attributed to the loose, ordered porous structure, the large specific surface area, the catalysis of the Cr2O3, and the synergistic effect of p-n heterojunction structure.