ZnO nanostructures with various morphologies and sizes were successfully prepared via a hydrothermal method. The influence of precursor concentration, reaction time, solvent, reaction temperature, annexing agent and alkali source on the morphology and structure was elucidated systematically. The preferential growth of ZnO crystal along C-axis direction was obvious when the precursor concentration was low. A balance between growth and dissolve existed during the process of forming ZnO. The solvent of water-methanol would make for the generation of products with a big size and regular morphology. The adsorption of CTA(+) from the additive of cetyltrimethyl ammonium bromide (CTAB) and hydroxyl groups from polyethylene glycol (PEG400) on ZnO would slow down the preferential growth rate along C-axis direction, leading to rod-like products with smaller aspect ratios. When the concentration of NaOH was increased to a certain degree, the growth rate of ZnO was slower than the decomposition rate, leading to appearance of irregular grain-like products. (C) 2013 Elsevier Ltd. All rights reserved.