ZnSb₂O₄ nanoparticles with an average size of about 53 nm are synthesized by a facile hydrothermal method. The humidity sensing characteristics of the devices based on our ZnSb₂O₄ nanoparticles are investigated systematically. Such humidity sensors show excellent performance with ultra-high sensitivity, fast response/recovery speed, a wide range of relative humidity (RH) response, and excellent stability and reversibility. The responsive mechanisms in the low and high humidity ranges are also analyzed and simulated.