In this work, nano-sized ZnO particles were prepared by a direct precipitation method with Zn(NO3)(2)center dot 6H(2) O and NH3 center dot H2O as raw materials, and the impact of the synthesis process was studied. The optimal thermal calcined temperature of precursor precipitates of ZnO was obtained from the differential thermal analysis (DTA) and the thermal gravimetric analysis (TGA) curves. The purity, microstructure, morphology of the calcined ZnO powders were studied by X-ray diffraction (XRD), energy dispersive X-ray spectrum (EDS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The synthesized ZnO powders had a wurtzite structure with high purity. The final products were of flower-like shape and the nanorods which consisted of the flower-like ZnO bunches were 20-100 nm in diameter and 0.5-1 mu m in length. The effect of process conditions on the morphology of ZnO was discussed. (C) 2012 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.