We report a systematic trend in the structural evolution of Pt-n clusters based on the first principle calculation. We show that up to n = 9, Pt-n clusters favor planar geometries and a structural transition to non-planar geometries occur at n = 10, which further evolves into cubic structures for larger clusters. Based on the stability analysis, it is found that n = 6 and 10 are more stable than others. The bonding analysis showed that an enhanced p-orbital contribution causes the structural transition from two to three dimensional geometries. (C) 2007 Elsevier B.V. All rights reserved.