The melting properties of size-selected isolated silver nanoparticles of N = 13-3871 atoms are studied by using molecular dynamics simulations, Three distinctive melting mechanisms are identified. The melting of Ag258-3871 can be explained well by the surface premelting models (SPMs), while the "melting" of Ag13-178 may be described as a transition from a low-energy solidlike structure at low temperatures to a higher-energy liquidlike structure at high temperatures. Acting as a connecting link between such two distinctive melting mechanisms, a new intermediate melting mechanism, in which the melting temperature T-m depresses very slowly while the latent heat of fusion Deltau(ls) has a great enhancement with N decreasing, is identified in Ag120-240.