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Herein we present the successful synthesis of aligned arrays of single-crystalline, 6-fold-symmetrical, hierarchical ZnO nanostructures via a two-step vapor-phase transport method. The X-ray diffraction and transmission electron microscopy results illustrate that the backbones of the as-grown product have excellent orientation along the [001] direction, and the branches epitaxially grow on the backbone along the ⟨100⟩ direction. At room temperature, the 6-fold-symmetrical hierarchical ZnO nanostructure arrays exhibit a very strong green luminescence centered at 515 nm. The field emission measurements show that they have a turn-on field of 5.6 V/μm and field-enhancement factor of 1351, which indicate their potential application in field emission nanodevices.