The transition from the planar to three-dimensional structures in Au clusters occurs at the cluster consisting of 15 An atoms, which is predicted based on the first-principles density functional theory (DFT) calculations including the spin-orbital coupling. The results show that the spin-orbit coupling does not alter the relative stability of Au clusters but increases the binding energy of the cluster by about 0.08 eV/atom for all the clusters studied here. The energy gap between the highest occupied and the lowest unoccupied orbitals, on the other hand, decreases when the spin-orbit coupling is included. (C) 2004 Elsevier B.V. All rights reserved.