Single crystalline zinc oxide (ZnO) nanowires have been grown on Si (100) substrates by a vapor-liquid-solid (VLS) process at temperatures in the range 850-950℃ in an inert atmosphere. The VLS-grown ZnO nanowires have been characterized in detail using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and photoluminescence spectroscopy (PL). The XRD studies revealed that the ZnO nanowires had wurtzite structure (hexagonal) with well-defined growth along [0001] direction. The composition analysis by EDX indicated the presence of small amounts of Si codeposited on the ZnO nanowires. The microscopic studies revealed a tilted configuration for ZnO nanowires on Si (100) with diameters in the range 60 to 100 nm and lengths varying between 1 to 3 μm. A strong ultraviolet emission has been observed for the ZnO nanowires as evidenced by the photoluminescence spectra at a wavelength of 381 nm.