In order to enhance the gas response of polypyrrole to NO2, the polypyrrole/Fe2O3 nanocomposites are synthesized by one-step hydrothermal route. The presence of ferric oxide in composites is demonstrated by XPS, HRTEM and TG analyses. The polypyrrole/Fe2O3 sensor exhibits high selectivity and response to NO2 at 50 degrees C. Compared with other polypyrrole/metal oxide materials, the polypyrrole/Fe2O3 materials are easy to be synthesized, and the gas sensor has a higher response of 220.7%, lower detection limit of 0.1 ppm and good linear relationship when the NO2 concentrations range from 0.1 ppm to 10 ppm. The gas response is greatly improved in comparison with the pure polypyrrole and Fe2O3. The reason for the improved response is also discussed. (C) 2019 Elsevier Inc. All rights reserved.