For　Pd-based　alloy　catalysts,　the　selection　of　metallic　alloying　elements　and　the　construction　of　composition-gradient　surface　and　subsurface　layers　are　critical　in　achieving　superior　electrocatalytic　activities　in,　e.g.,　the　oxygen　reduction　reaction　(ORR).　Based　on　the　Pd-containing　alloy,　highly　monodispersed　PdCuNi　ternary　alloy　nanocrystals　are　prepared　through　a　wet-chemical　approach,　and　a　solution-based　oxidative　surface　treatment　protocol　is　utilized　to　activate　the　surface　of　the　nanocrystals.　A　drastically　enhanced　ORR　activity　can　be　achieved　by　removing　the　surface　Ni　and　Cu　atoms　through　the　surface　treatment　protocol.　The　treated　catalyst　demonstrates　a　mass　activity　of　0.45　A　mg(Pd)(-1)　in　alkaline　medium,　5　and　2.4　times　those　of　commercial　Pt/C　and　Pd/C,　respectively.　The　first-principle　calculation　result　suggests　the　critical　roles　of　the　coexistence　of　Ni　and　Cu　atoms　and　their　synergistic　interaction　beneath　the　outmost　pure　Pd　layer　in　optimizing　the　oxygen　binding　energy　for　ORR.　The　calculation　also　suggests　that　the　optimal　binding　energy　of　oxygen　requires　an　appropriate　Ni/Cu　ratio　in　the　subsurface　layer.　This　work　demonstrates　a　class　of　high-performance　Pt-free　ternary　alloy　ORR　catalysts　and　may　provide　a　general　guideline　for　the　structural　design　of　Pd-based　ternary　alloy　catalysts.