Size-controlled ZrO2 nanorods were prepared via a facile hydrothermal treatment approach in the presence of NH4F as mineralizer. The effects of the type and concentration of mineralizers on the particle size and dispersibility of ZrO2 nanorods were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), N-2 adsorption-desorption measurements (BET), and X-ray photoelectron spectroscopy (XPS), confirming the essential role of F- in tuning the particle size. Humidity sensors based on ZrO2 nanorods with different sizes exhibit different sensitivity depending on their proportion of surface adsorbed oxygen. High sensitivity, linear response, small hysteresis, and rapid response-recovery behavior (5 s for adsorption and 38 s for desorption) make ZrO2 prepared by our method a good candidate for application in humidity sensor. The complex impedance spectra were used to elucidate its humidity sensing mechanism in detail. (C) 2013 Elsevier Inc. All rights reserved.