Uniform cake-like YBO3:Eu3+ assemblies were successfully synthesized by a poly(vinylpyrrolidone)-assisted hydrothermal method. The products were characterized by X-ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy. The results revealed that these particles were actually composed of many circular plates, which aligned well along their longitudinal direction. A high annealing temperature (>= 1100 degrees C) led to the formation of a new phase (Y3BO6) and the disappearance of the cake-like morphology. Photoluminescence measurements indicated that the cake-like YBO3:Eu3+ exhibited a higher ratio (R/O value) compared with the bulk YBO3:Eu3+, and the emission intensity enhanced with increasing annealing temperature up to 1000 degrees C and then declined with further increasing temperature due to the formation of a new phase.