We have studied the mobility of small Ni clusters on a crystalline surface by molecular dynamics simulation. We chose the anisotropic Au(I I 0)-(l x 2) reconstructed surface as the substrate to host the atom clusters. Similar to Au/Au(I I 0)-(l x 2), we found that in-channel Ni adatom diffusion takes place by jumping in the trough and on the sidewall, the Ni dimer by leapfrog and concerted jump. However, the Ni trimer can diffuse via rotation. For the larger cluster with a sphere-like shape, we find the cluster can roll on the surface, which can lead to a large diffusion constant. (C) 2003 Published by Elsevier Science B.V.