Using embedded-atom-method (EAM) potential of Ag/Cu heterogeneous system, structural stabilities and diffusion behaviors of small Cu clusters on Ag (1 1 1) surface have been investigated by molecular dynamics studies. The binding energies, the effective diffusion barriers and the corresponding prefactors for Cu clusters have been calculated. Structural stabilities and the diffusion properties of small Cu clusters show significant magic size effects: the trimer and heptamer clusters with relatively higher effective diffusion barriers are more stable than the other sizes. Moreover, the dimer's and trimer's rotation mechanism have been investigated in this paper as well. (C) 2012 Elsevier B. V. All rights reserved.