Au nanoparticles are hydrothermally loaded on the ZnO nanorod arrays (NRs), and the characteristics of Au can be modulated by controlling the precursor concentration. The morphology, crystallinity and composition of Au/ZnO nanorods are characterized by SEM, XRD and TEM. Moreover, the growth behavior and mechanism of Au nanoparticles with different sizes and populations on ZnO are proposed and clearly elucidated. Furthermore, the influence of Au nanoparticle decoration on ZnO NRs used for CO gas sensor is discussed in terms of its surface configuration and the related sensitization mechanisms. It is found that the gas sensitivity toward C2H5OH is superior to that of H-2 and CO in the Au/ZnO NRs, especially for higher concentrations of analyte, and the result is ascribed to the difference in electron donating effect and the increasing quantity in chemisorbed oxygen by the catalytic effect of Au nanoparticles. (C) 2013 The Electrochemical Society. All rights reserved.