CuO nanowires were prepared by thermal oxidation methods from copper substrates. Morphology of CuO nanowires, i.e. diameter, length could be controlled by varying annealing temperature in the thermal oxidation process. The diameters of CuO nanowires ranged from 30 nm to more than 100 nm and the lengths were up to several microns. The obtained nanowires were characterized with Xray diffraction measurement, scanning electron microscopy, and Raman spectroscopy. The XRD results shows that CuO nanowires had monoclinic structure while position and width of Raman A(1g) peaks of the samples were closely related to size and density of the nanowires. Growth mechanism of CuO nanowires were suggested based on the energy dispersive spectroscopy and scanning electron microscope images.