Anisotropically structured upconversion nanocrystals capable of exhibiting bright upconversion emission properties are a promising new class of high performance optical materials. In this study, we investigate a facile synthetic method for the new nanoplate structure of YF3:Yb3+/Er3+ with enhanced luminescence intensity. The shape of YF3:Yb3+/Er3+ nanocrystals can be controlled by changing the synthesis conditions of the NaOH concentration, reaction time, and surfactant. The concentration of NaOH determines the final structure of YF3:Yb3+/Er3+. By increasing the NaOH concentration from 0.25 mmol to 2.5 mmol, YF3:Yb3+/Er3+ nanoplates transform into NaYF4:Yb3+/Er3+ nanoparticles; in the absence of NaOH, the nanoplate structure of YF3:Yb3+/Er3+ changes to particles. The YF3:Yb3+/Er3+ nanoplates show luminescence efficiency much greater than that of the spherical YF3:Yb3+/Er3+ nanocrystals.