A fiber-optic hydrogen (H2) sensor based on tilted fiber Bragg grating (TFBG) deposited with Pd/tungsten oxide (WO3) nanofilm is proposed and demonstrated. The tilted grating planes of the employed TFBG can resonantly excite a series of cladding modes and generate a strong evanescent field, interacting with the Pd/WO3 nanocoating possessing an effective refractive index related to the H2 concentration dependence. Pd/WO3 nanocoating endows TFBG with the capability to sense H2 concentration. Experimental results show that the Pd/WO3 nanofilm-deposited grating presents a response sensitivity of 0.13 dB/% in the H2 concentration range of 0%–3%, by tracking the intensity and wavelength of a specific cladding mode. Through monitoring of the intensity evolution under different H2 concentrations, the sensor exhibits a response time of 85 s and a recovery time of 118 s at a H2 concentration of 0.5%. The fast response and easy fabrication of the proposed TFBG sensor may enable the optical fiber device for promising applications, including fuel cell vehicles, biomedical, and petrochemicals.