Flower-like ZnO was synthesized in a simple chemical bath method. This ZnO structure modified by a controllable density of Au nanoparticles with an average diameter of 40 nm was achieved with hydrothermal process. The Uv-vis adsorption spectra of Au nanoparticles shifted a little, indicating the interaction between ZnO and Au nanoparticles, which led to excellent gas sensing performance. ZnO modified by Au nanoparticles with weight percent of 6 % showed that the optimum gas response to acetone and the gas response was nearly 17 times higher than that of pure ZnO.