ZnO nanowires were grown oil Si (100) substrates with and Without Au catalyst by chemical vapor deposition employing the vapor-liquid-solid (VLS) and vapor-solid (VS) mechanisms, respectively. The diameters of the resulting nanowires were in the range 80-150 nm with typical length about 10 mu m. The near-band-edge (NBE) emission of Zoo nanowires grown with and Without catalyst was observed at 382 nm and 386 nm, respectively. The intensity of the NBE emission of ZnO nanowires grown without file catalyst was higher than that of file green luminescence. By sharp contrast, the intensity of the NBE emission of ZnO nanowires grown with catalyst was lower than that of green luminescence. The X-ray diffraction (XRD) spectrum of file ZnO nanowires grown without catalyst exhibited a peak intensity of c-plane 5 times higher than that of m-plane and 10 times higher than that of a-plane. However, the XRD spectrum of file ZnO nanowires grown with catalyst exhibited a peak intensity of file c-plane about 1.5 times higher than that of the Ill-plane and 4 times higher than that of-a-plane intensity. Thus, the ZnO nanowires grown without catalyst have a preferential orientation along the c-axis direction. Our results show that the catalyst strongly effects optical and structural properties of the ZnO nanowires. (C) 2009 Elsevier Ltd. All rights reserved.