Oxide-supported　transition　metal　systems　have　been　the　subject　of　enormous　interest　due　to　the　improvement　of　catalytic　properties　relative　to　the　separate　metal.　Thus　in　this　paper,　we　embark　on　a　systematic　study　for　Pdn　(n　=　1-5)　clusters　adsorbed　on　TiO2(110)　surface　based　on　DFT-GGA　calculations　utilizing　periodic　supercell　models.　A　single　Pd　adatom　on　the　defect-free　surface　prefers　to　adsorb　at　a　hollow　site　bridging　a　protruded　oxygen　and　a　five-fold　titanium　atom　along　the　[110]　direction,　while　Pd　dimer　is　located　on　the　channels　with　the　Pd-Pd　bond　parallel　to　the　surface.　According　to　the　transition　states　(TSs)　search,　the　adsorbed　Pd　trimer　tends　to　triangular　growth　mode,　rather　than　linear　mode,　while　the　Pd4　and　Pd5　clusters　prefer　three-dimensional　(3D)　models.　However,　the　oxygen　vacancy　has　almost　no　influence　on　the　promotion　of　Pdn　cluster　nucleation.　Additionally,　of　particular　significance　is　that　the　Pd-TiO2　interaction　is　the　main　driving　force　at　the　beginning　of　Pd　nucleation,　whereas　the　Pd-Pd　interaction　gets　down　to　control　the　growth　process　of　Pd　cluster　as　the　cluster　gets　larger.　It　is　hoped　that　our　theoretical　study　would　shed　light　on　further　designing　high-performance　TiO2　supported　Pd-based　catalysts.　©　2012　CAS/DICP.