The dendrite-like CuO nanostructures, consisting of a rod-like main stem and some rod-like sub-branches, have been synthesized by a simple ethylene glycol (EG) assisted hydrothermal method. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) patterns indicate that the dendrite-like CuO nanostructures are of monoclinic phase and the individual branch of CuO is single crystalline in nature. The effects of the growth conditions such as temperature and pH value on the morphology and structures of CuO have also been investigated. It is indicated that different temperature and pH value result in the morphology and structure evolution of CuO. Moreover, a possible mechanism for the morphology and structures evolution of CuO has been primarily presented. (C) 2007 Elsevier Ltd. All rights reserved.