Structural stability and energetics of nickel clusters, Ni_N (N =3-459), have been investigated by molecular-dynamics simulations. A size-dependent empirical model potential energy function has been used in the simulations. Stable structures of the microclusters with sizes N = 3-55 and clusters generated from fcc crystal structure with sizes N = 79-459 have been determined by molecular-dynamics simulations. It has been found that the five-fold symmetry appears on the surface of the spherical clusters. The average coordination number shows a size-dependent characteristic, on the other hand the average nearest-neighbor distance does not show a size-dependence.