The nanowires of gallium nitride were synthesized on Si wafer by ammoniating reaction in the absence of catalyst. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission (HRTEM) and photoluminescence (PL) spectrum were used to characterize the samples. The results showed that the formed nanowires are straight and smooth, with even diameters ranging from 5 to 20 nm and length up to several tens of micrometers. The single nanowire is uniform along radial orientation. The nanowires are single crystal hexagonal wurtzite GaN and possess the growth direction [001]. They have high crystal quality and good properties in PL. The technique used in this paper could effectively avoid the entrance of impurity and thus prepare GaN nanowires with high purity. (c) 2006 Elsevier B.V. All rights reserved.