Single crystalline wurzite GaN nanowires were synthesized through ammoniating Ga2O3/Ta films by RF magnetron sputtering. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED) and photoluminescence (PL). The results show that the nanowires have a hexagonal wurtzite structure with diameters ranging from 20 nm to 60 nm and lengths typically up to 10 μm. The PL spectrum exhibits a strong UV light emission at 363 nm. The growth mechanism of the crystalline GaN nanowires is discussed briefly