A novel solvothermal oxidation route has been used to prepare hydroxyl-free nanocrystalline zinc oxide via the oxidation of zinc powder with trimethylamine N-oxide (Me3N --> O) or 4-picoline N-oxide (4-picN --> O) in different organic solvents under dry nitrogen atmosphere. It is found that both oxygen sources and solvents have great effect on morphologies and sizes of nanocrystalline ZnO. The role of the small amount of water in wet solvent in the formation of nanocrystalline ZnO is also studied. The products are characterized by X-ray diffraction, transmission election microscopy. Possible mechanisms of the formation of the nanocrystalline ZnO are discussed. (C) 2003 Elsevier Science B.V. All rights reserved.