Highly uniform pancake-like YBO(3) hierarchical architectures have been successfully prepared by a designed two-step hydrothermal method. Yttrium precursor microprisms were first synthesized according to a simple hydrothermal route. Subsequently, nearly monodisperse multilayered YBO(3) products with a pancake-like shape were synthesized at the expense of the precursor during the hydrothermal process. The whole process was carried out under aqueous conditions without the use of any organic solvent, surfactant, or catalyst. The conversion process from the precursor to YBO(3) products has been investigated by time-dependent XRD experiments. Extending this method, other LnBO(3) (Ln=Ho, Er, Tm, Yb) samples with well-defined shape and dimensionality have also been obtained by a similar synthetic process. The luminescence colors of YBO(3) samples co-doped with Eu(3+) and Tb(3+) under ultraviolet or low-voltage electron beam excitation can be tuned from red, through yellow and green-yellow, to green by simply adjusting the relative doping concentrations of the activator ions. This merit of multicolor emissions in the visible region endows materials of this kind with potential application in the fields of light-display systems and optoelectronic devices.