A thin-film-based optical fiber Fabry-Perot interferometer that consists of ZrO2 and SiO2 porous thin films is designed and fabricated by electron beam physical vapor deposition. Since the SiO2 porous thin film has the capability of water adsorption, the proposed Fabry-Perot interferometer is appropriate to detect humidity. Experimental results show that the prepared sensor has a humidity detection range from 0.06% RH to 70% RH. A cycling test shows that the humidity sensor has a responding or recover time of 4 s and good repeatability among different humidity environments. Especially, the proposed humidity sensor is insensitive to temperature variation and suitable for the detection of low relative humidity.