KLaF4　nanocrystals　(NCs)　co-doped　with　2%Er3+(fixed)　and　varied　Yb3+　doping　mole　fractions　(10%,　14%,　18%)　were　synthesized　by　hydrothermal　method.　The　samples　were　annealed　in　argon　at　300°C　for　1.5　h.　The　crystal　structure　and　morphology　of　the　samples　were　confirmed　by　X-ray　diffraction　(XRD)　and　transmission　electron　microscopy　(TEM),　respectively.　The　optical　properties　of　the　samples　were　evaluated　by　diffuse　reflectance　spectra　and　up-conversion　photoluminescence　spectroscopy　with　the　average　fluorescent　lifetimes　of　2H11/2　level　under　laser　excitation　at　980　nm.　The　results　show　hexagonal　KLaF4:　Er3+,　Yb3+　NCs　are　successfully　obtained,　which　have　a　longitude　of　about　130　nm　and　a　diameter　of　28　nm　for　the　annealed　sample.　The　diffuse　reflection　spectra　indicate　that　the　absorbtion　at　around　973　nm　is　enhanced　with　the　increase　of　Yb3+　mole　fraction　while　Er3+　mole　fraction　is　fixed.　The　near-infrared　light　at　980　nm　can　be　up-converted　to　green　and　red　light.　Furthermore,　both　the　intensities　of　the　red　and　green　light　and　the　average　fluorescence　lifetimes　for　2H11/2　level　were　decreased　with　the　increase　of　Yb3+　ion　concentration　in　KLaF4:　Er3+,　Yb3+　NCs.　In　addition,　the　effect　of　Yb3+　doping　concertration　on　the　intensity　of　up-conversion　luminescence　and　the　average　fluorescence　lifetimes　for　2H11/2　level　were　briefly　clarified.