Large-scale GaN nanowires were synthesized on Si(111) substrates through ammoniating Ga2O3/V films. The as-grown products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results reveal that the grown GaN nanowires have a smooth and clean surface with diameters ranging from 20 nm to 60 nm and lengths of about several tens of micrometers. The results of HRTEM and selected-area electron diffraction (SAED) show that the nanowires are pure hexagonal GaN single crystal. The photoluminescence (PL) spectrum indicates that the GaN nanowires have good emission property. The growth mechanism is discussed briefly.