Highly uniform and monodispersed pure hexagonal phase NaReF4 (Re = Y, Pr–Nd, and Sm–Yb) nanocrystals with well-defined morphologies, including pills, rods, spheres, tubes, and plates, were systematically synthesized by a facile solution-based hydrothermal method using oleic acid as a stabilizing agent. Crystal phase, shape and size can be tuned readily by simply adjusting the molar ratio of F/Re and reaction temperature. Detailed experimental studies revealed that NaReF4 hosts strongly tend to form hexagonal phase nanocrystals with increasing rare earth ion radius. Based on the studies on crystal phase control and shape evolution of NaReF4 nanocrystals, the whole growth mechanism of nanocrystals can be concluded as a kinetic and thermodynamic growth process. Simultaneously, highly efficient up-conversion luminescence under 980 nm excitation was realized, such as eye-visible red, green, and blue up-conversion luminescence generated from NaYbF4 host doped with Er3+, Ho3+, and Tm3+, respectively. Due to their unique up-conversion luminescence, the highly uniform and monodispersed nanocrystals can be applied for biolabels, colour displays, light-emitting diodes, and solid-state lasers.