Pd2+-doped ZnO nanotetrapods were prepared and studied for the humidity detection application. The humidity sensors developed were featured by combination of a quartz crystal microbalance (QCM) as a transducer and Pd2+-doped ZnO nanotetrapods as a sensing element. The ZnO nanotetrapods were synthesized by evaporating highly pure zinc pellets (99.999%) at 900 degrees C in air and PdCl2 was doped on by traditional solution mixing process. Then the mixed solution distributed onto the electrode surfaces of the quartz crystal at room temperature. Pd2+-doped ZnO nanotetrapods were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The experimental results indicated that the response of the sensors varied with the different dosage PdCl2. Linear regression algorithm was used for evincing the highly linear behavior of the Pd2+-doped ZnO nanotetrapods sensor. In this humidity sensing system, the Pd2+-doped ZnO nanotetrapods sensing material coated on the gold electrode of QCM showed good sensitivity (similar to 74.24324 Hz/%RH (relative humidity)), reproducibility, linearity (R-2 = -0.98834), short response and recovery time (less than 5 s). (c) 2006 Elsevier B.V All rights reserved.