H2S gas sensor based on alpha-Fe2O3 nanoparticles was fabricated by post-thermal annealing of Fe3O4 precursor which was synthesized using a facile hydrothermal route. The characteristic techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were adopted to characterize the chemical composition and microstructure of the obtained samples. Gas-sensing performance of the sensor was investigated at different operation temperatures from 100 degrees C to 400 degrees C. Results showed that the sensor exhibited the best sensitivity, reproducibility and long-term stability for detecting H2S gas at an operating temperature of 300 degrees C. The detection limit towards H2S gas was 0.05 ppm, and the response time and recovery time was 30s and 5 s, respectively. In addition, sensing mechanism of the sensor towards H2S was discussed. (C) 2015 Elsevier B.V. All rights reserved.