By heating pure zinc powder at low temperature, two kinds of ZnO nanostructures with different morphology and diameter were grown on silicon (1 0 0) substrates. Scanning electron microscopy images show that ZnO nanorods and ZnO nanowires have been obtained. XRD demonstrates that the grown ZnO nanostructures are hexagonal wurtzite crystalline. The electron field emission properties were studied for both kinds of samples. The ZnO nanorods sample has a low turn-on field at 3.6 V/μm owing to better alignment, while the field to obtain a current density of 1 mA5cm-2 is higher (at 11.2 V/μm) than that of the nanowires sample due to bigger diameter. For nanowires sample, an emission current of 1 mA5cm-2 is achieved at 8.2 V/μm which is lower than that of ZnO nanorods owing to better high aspect ratio.