Metal growth processes of Pd clusters on mica were studied using atomic force microscopy (AFM). The Pd clusters formed were hemispherical until the cluster size was below 1.0 10 4 atom cluster - 1 . However, when the cluster size exceeds this value, the cluster shape was dramatically changed to thinner and flatter. Here, the Pd clusters were self-ordered into microcrystals. These phenomena can be explained in terms of the unit surface energy of the clusters.