Plasmon　induced　hot　carrier　transfer　is　a　promising　novel　approach　for　solar　energy　conversion,　but　its　practical　application　is　often　hindered　by　its　low　efficiency.　This　work　demonstrates　an　unprecedented　quantum　efficiency　of　plasmonic　hot-electron　transfer　of　up　to　53　+/-　2%　from　1.7　nm　silver　nanoparticles　to　anatase　nanoporous　TiO2　films　at　400　nm　excitation.　This　efficient　hot-electron　transfer　consists　of　contributions　of　both　hot　electrons　generated　by　plasmon　decay　through　exciting　Ag　intraband　transitions　and　Ag-to-TiO2　interfacial　charge-transfer　transitions.　The　efficiencies　of　both　pathways　increase　at　smaller　Ag　particle　sizes　from　5.9　to　1.7　nm,　suggesting　that　decreasing　particle　sizes　is　a　promising　way　toward　efficient　plasmonic　hot-carrier　extraction.