Large-scale cupric oxide (CuO) nanowires have been synthesized by thermal evaporating copper foils in 02 ambient at the temperatures from 300degreesC to 900degreesC. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were performed on the study of the CuO nanowires. XRD studies reveal the possibility of two-steps of nanowire formation; HRTEM image shows the bicrystal structure of the nanowire; SEM studies indicate the relationship between the morphology of the prepared nanowires and the growth conditions. The growth of the nanowires seems to be vapor-solid (VS) mechanism. (C) 2003 Elsevier B.V. All rights reserved.