Monodisperse sodium yttrium fluoride corn sticks with hexagonal nanostructure were successfully prepared by a facile and repeatable precipitation transformation method. The phase and morphology of the products were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The growth mechanism was studied, indicating that the initial generated Y(OH)3 gradually translated into YF3 and then transformed into corn stick-like H-NaYF4 nanoparticles owing to the crucial role of fluorine ions in the solution. The up-conversion (UC) luminescence properties of H-NaYF4:20%Yb3+,2%Er3+ nanocrystals were discussed. The intensive green emission in the range of 510–570 nm was attributed to the (2H11/2, 4S3/2)→4I15/2 transition and the weaker red emission between 640 and 680 nm was originating from the 4F9/2→4I15/2 transition.