Tungsten trioxide nanopetal with Fe2O3 composite films were synthesized by dealloying the W-Fe alloy film in HCl aqueous solution; nano-Pd particles were directly electrochemical deposited on the surface of dealloying films in a micro-emulsion system and following thermal oxidation in air. The structure, morphology, chemical composition and quality of the prepared WO3 nanopetal with Fe2O3 composite films were characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The results showed that the thickness of the WO3 nanopetals were less than 50 nm, which were monoclinic phase after controlled thermal oxidation process, and the nano-Pd particles were evenly dispersed on the WO3 film surface with controlled diameters ranging from 20 to 40 nm. The sensors were tested for 25-2000 ppm H2 at temperatures from 50 to 200 degrees C; and the H2 sensing properties of Pd loading (1.54 at.%) WO3-Fe2O3 composited films exibited the best response at the low working temperature of 125 degrees C.