Porous α-Fe 2 O 3 nanoparticles were synthesized by simple annealing of β-FeOOH precursor derived from a facile hydrothermal route, the structures and morphologies of the as-prepared product were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results showed that the average crystallite size of the obtained porous α-Fe 2 O 3 was 34 nm and exits numerous irregularly distributed pores with a diameter varying from 2 nm to 10 nm on the particle surface. The gas-sensing properties of the sensor based on porous α-Fe 2 O 3 nanoparticles were investigated, and the result showed that the sensor exhibited a high performance in hydrogen sulfide (H 2 S) detection at room temperature. The highest sensitivity reached 38.4 for 100 ppm H 2 S, and the detection limit was as low as 50 ppb. In addition, the response of the sensor towards other gases including C 2 H 5 OH, CO, H 2 and NH 3 indicates the sensor has an excellent selectivity to detection H 2 S gas. Finally, the sensing mechanism of the sensor towards H 2 S was also discussed. [ABSTRACT FROM AUTHOR]