Pt-Fe2O3 composite nanoceramics were prepared from Pt and Fe2O3 nanoparticles through traditional pressing and sintering. SEM analyses showed that numerous nanosized pores were present in the ceramics and Fe2O3 grains were around 30nm in size. Sensors based-on the nonoceramics were found to show strong responses to hydrogen at room temperature. To 5% H2 in N2, the sensitivity was over 90, and the response and recovery times were 20s and 30s, respectively. To explore the room-temperature hydrogen sensing mechanism, hydrogen concentration in surrounding N2 was decreased from 5% to 0. The resistance of the sensors was found to show no response to the hydrogen concentration variation. It indicates that hydrogen-induced decrease in resistance of Fe2O3 results from the reaction between chemisorbed oxygen on Fe2O3 and hydrogen at room temperature with the catalytic effect of Pt. Fe2O3 based ceramics are quite different from TiO2based ceramics in room-temperature hydrogen sensing properties and mechanism, and systematic investigations should be conducted on room-temperature hydrogen sensing of various metal oxide semiconductor ceramics.