Monodispersed beta-NaYF4 spindlelike mesocrystals have been successfully synthesized directly from Y(OH)(x)F3-x as a precursor via a facile route. Detailed structural analyses demonstrated that the crystal framework structures of Y(OH)(x)F3-x and beta-NaYF4 were identical. A possible mechanism based on in situ ion-exchange transformation has been proposed. The monodispersed beta-NaYF4 can be obtained through carefully controlled synthesis of the precursor. The photoluminescence properties of the beta-NaYF4 doped with various rare earth ions (such as Yb/Er, Yb/Tm, Pr, Nd, Sm, Eu, Tb, Dy, and Ho) were investigated and multicolor emission was achieved.