CdO decorated flower-like ZnO hollow microspheres were successfully prepared via a two-step hydrothermal strategy. CdO nanoparticles (similar to 12 nm) equably loaded on the surfaces of ZnO nanosheets, which could be clearly observed from SEM and TEM images. The results of X-ray photoelectron spectroscopy and H-2 temperature-programmed reduction (H-2-TPR) indicated that the amount of chemisorbed oxygen was increased after the introduction of CdO nanoparticles. Compared with the flower-like ZnO hollow microspheres, the 2.6 mol% CdO:ZnO heterostructure composites exhibited highest response (65.5) to 100 ppm ethanol at 250 C-omicron, which was about 16 folder higher than that of pure ZnO at the same operating temperature of 250 C-omicron. Significantly, the detection limit of the 2.6 mol% CdO:ZnO heterostructure could reach ppb level (500 ppb). The mechanism of the enhanced ethanol sensing was also discussed systematically.