Hollow　nanoparticles　with　large　specific　surface　area　and　high　atom　utilization　are　promising　catalysts　for　the　hydrogen　evolution　reaction　(HER).　We　describe　herein　the　design　and　synthesis　of　a　series　of　ultra-small　hollow　ternary　alloy　nanostructures　using　a　simple　one-pot　strategy.　The　same　technique　was　demonstrated　for　hollow　PtNiCu　nanoparticles,　hollow　PtCoCu　nanoparticles　and　hollow　CuNiCo　nanoparticles.　During　synthesis,　the　displacement　reaction　and　oxidative　etching　played　important　roles　in　the　formation　of　hollow　structures.　Moreover,　our　hollow　PtNiCu　and　PtCoCu　nanoparticles　were　single　crystalline,　with　an　average　diameter　of　5　nm.　Impressively,　ultra-small　hollow　PtNiCu　nanoparticles,　containing　only　10%　Pt,　exhibited　greater　electrocatalytic　HER　activity　and　stability　than　a　commercial　Pt/C　catalyst.　The　overpotential　of　hollow　PtNiCu　nanoparticles　at　10　mA　cm(-2)　was　28　mV　versus　reversible　hydrogen　electrode　(RHE).　The　mass　activity　was　4.54　A　mg(Pt)(-1)　at　-70　mV　versus　RHE,　which　is　5.62-fold　greater　than　that　of　a　commercial　Pt/C　system　(0.81　A　mg(Pt)(-1)).　Through　analyses　of　bonding　and　antibonding　orbital　filling,　density　functional　theory　calculations　demonstrated　that　the　bonding　strength　of　different　metals　to　the　hydrogen　intermediate　(H-*)　was　in　the　order　of　Pt　＞　Co　＞　Ni　＞　Cu.　The　excellent　HER　performance　of　our　hollow　PtNiCu　nanoparticles　derives　from　moderately　synergistic　interactions　between　the　three　metals　and　H-*.　This　work　demonstrates　a　new　strategy　for　the　design　of　low-cost　and　high-activity　HER　catalysts.