The structural stability and melting characteristics of hexagonal GaN nanowires are investigated using molecular dynamics simulations. The GaN nanowire with (10−10) facets is energetically more stable than that with (11−20). The melting temperature of GaN nanowires with (10−10) facets is much lower than that of bulk GaN and decreases with decreasing diameter, due to the surface energy increased. The structural transition of GaN nanowires with increasing temperature and the size effect of the melting temperature are also studied.