A synthesis of LaF3:0.04Yb3+,0.01Er3+ nanocrystals with oleic acid as a capping iigand was presented. The X-Ray Diffraction (XRD) pattern indicated that the power was a single hexagonal phase. Transmission Electron Microscopy (TEM) demonstrated that the average size of the nanocrystals was less than 10 nm, with a narrow size distribution. The nanocrystals were dispersible in nonpolar solvents and form a fully transparent colloidal solution, and the solution was stable for several months without any aggregates. The Yb3+-Er3+ codoped nanocrystal colloidal solution exhibited a bright green upconversion fluorescence under 980 nm excitation from a diode laser. The nanocrystals were potentially applicable in biolabeling and bioimaging.