Upconversion　nanocrystals　(UCNCs)　hold　promise　for　bioimaging,　solar　cells,　photocatalysis　and　volumetric　displays.　However,　their　upconversion　luminescence　intensities　are　usually　low　due　to　the　weak　and　narrowband　near-infrared　absorption　of　lanthanide　ions.　Herein,　we　introduce　and　validate　a　strategy　to　hugely　enhance　upconversion　luminescence　intensity　by　using　an　organic　near-infrared　dye　as　an　antenna　to　sensitize　core/shell　UCNCs.　The　dye　can　increase　absorptivity　and　broaden　the　absorption　spectrum　of　the　UCNCs.　Such　dye　sensitization,　in　combination　with　a　core/shell　structure,　can　tremendously　enhance　the　upconversion　luminescence　(UCL)　intensity　of　the　UCNCs.　The　UCL　intensity　of　dye-sensitized　UCNCs　excited　at　820　nm　is　800-folds　higher　than　that　of　pure　UCNCs　excited　at　980　nm.　Further　enhancement　can　be　obtained　by　optimization　of　the　dye　emission　and　UCNC　absorption　spectral　overlap.　Moreover,　the　proposed　approach　can　be　extended　to　cover　any　part　of　the　solar　spectrum　by　using　a　set　of　dyes.　This　work　provides　new　insights　into　the　efficient　enhancement　of　upconversion　luminescence　of　the　UCNCs　and　facilitates　their　applications.