The nanowire structure can be applied to a wide range of electronic and optical devices because of its electronconfinement effect and high specific surface area. In particular, oxide-based nanowires can be applied to various fields including solarcells. Copper oxide has various phases and many advantages, such as low cost and no toxicity. In particular, cuprous oxide (Cu2O) cantheoretically achieve a high conversion efficiency of ~20%. In this study, copper foil was annealed at various temperatures and copperoxide began to develop in the form of a nanowire at over 300°C. X-ray diffraction, scanning electron microscopy, and transmissionelectron microscopy confirmed that the nanowires grown at 400°C and 600°C crystallized in the stoichiometric Cu2O and CuO (cupricoxide) phases, respectively. This systematic work can contribute to the development of nanowire-based solar cells.