ZnO nanostructures hold substantial promise for gas-sensing applications owing to their outstanding ethanol sensing performance, yet their sensing performance toward NH3 has rarely been reported. Here, we report on a successful preparation of sunflower-like ZnO nanostructures and ZnO nanoparticle via a facile hydrothermal method, and demonstrate that the ZnO nanoflowers have high gas-sensing performances toward NH3 under a low concentration of 10-50 ppm. Further structural characterization reveals that the sunflower-like nanostructure comprises six triangles-like and one sphere-like nanostructures, and the triangle-like nanostructure is single crystalline with {001} crystal face. As a consequence of their unique morphology, the nanoflowers show much improved NH3 sensing performances than the nanoparticles with a high sensitivity of 49.5. (C) 2015 Elsevier B.V. All rights reserved.