Hexagonal phase NaYF4: Eu3+ materials were successfully synthesized by a facile EDTA-assisted hydrothermal route. The microstructure, morphology and luminescence property of the as-synthesized samples were characterized by XRD, XPS, SEM, TEM, HRTEM and photoluminescence (PL) spectra. The pristine NaYF4: Eu3+ microprisms have uniform size and morphology with 3-4 micrometers in length and ca. 500 nm in diameter. The annealing treatment afterwards achieved high crystallinity, and moreover, had a remarkable influence on morphologies of the NaYF4: Eu3+ sample. In comparison with the pristine sample, the annealed NaYF4: Eu3+ microcrystals had a markedly enhancement of down-conversion (DC) luminescence properties, which may be due to the high crystallinity and large surface roughness resulted from annealing treatment.