The field-emission properties of the ZnO nanotip arrays, nanowire arrays as well as Al-doped ZnO nanowires were investigated in detail. After comparison of the different morphologies, it was found that the morphology of the nanostructure ZnO materials has played a crucial role in their field emission performances, especially the turn-on field and the emission current density. Among them, the ZnO nanotip arrays have the lower turn-on field, higher current density, which is attributed to the small emitter radius on the nanoscale and the well vertical align on the substrates. It can effectively improve the field-emission property to dope aluminium in ZnO nanowires because of the carrier concentration increasing. which results in the increase of the field enhancement factor and the reduction of the work function. The emission stability is very good from the emission persistence measurement. (C) 2009 Elsevier Ltd. All rights reserved.