Gas sensors are devices that can convert the concentration of an analyte gas into an electronic signal. Zinc oxide (ZnO) is an important n-type metal oxide semiconductor which has been utilized as sensor for several decades. In recent years, there have been extensive investigations of nanoscale semiconductor gas sensors. The size reduction of ZnO sensors to nanometer scale provides a good opportunity to dramatically increase their sensing properties in comparison with their macroscale counterparts.<p> In this work, two kinds of ZnO nanostructures (nanowires and nanorods) were studied. ZnO nanowires were synthesized by electrodeposition while porous anodic aluminum oxide served as a growth template. Three types of ZnO nanowires with different diameters were obtained. Meanwhile, ZnO nanorods were prepared by a hydrothermal route from ZnO nanoparticle seeds. However, the aspect ratio (length/width) of nanorods was significantly smaller than that of nanowires. Both nanowires and nanorods were characterized by optical microscopy, scanning electron microscopy, powder X-ray diffraction, energy dispersive X-ray spectroscopy and energy dispersive spectroscopy.<p> The sensing performance of the synthetic ZnO nanostructures were investigated by three gases: saturated water vapour in air, saturated ethanol vapour in air, and carbon monoxide in air. Both ZnO nanostructures showed good sensitivity and selectivity to ethanol vapour. At high temperature, the ZnO nanosensors were up to seven times more responsive to ethanol vapour than water vapour and over 200 times more responsive to ethanol vapour than CO. Due to the size dependence, ZnO nanowires with the smallest diameter is considered the best sensor candidate among ZnO nanowires.<p> On the basis of previous work, Au/ZnO/Au multimetallic nanobarcodes were also synthesized by electrodeposition, and their sensing characteristics are to be investigated in the future.