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　Pd　n　(n　=　1-5)　clusters　adsorbed　on　TiO　2(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　Pd　4　and　Pd　5　clusters　prefer　three-dimensional　(3D)　models.　However,　the　oxygen　vacancy　has　almost　no　influence　on　the　promotion　of　Pd　n　cluster　nucleation.　Additionally,　of　particular　significance　is　that　the　Pd-TiO　2　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　TiO　2　supported　Pd-based　catalysts.　©　2012　CAS/DICP.