Monodispersed Ce³⁺-doped Y₃Al₅O₁₂ (YAG:Ce³⁺) nanospheres were synthesized through forced hydrolysis using a urea method, followed by thermal calcination processes, and their luminescence properties were examined. The crystallization of the YAG:Ce³⁺ phase and morphological evolutions after subsequent heat treatment were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) analysis revealed that the amorphous aluminum oxide layer played an important role in preventing necking between the particles during heat treatment. As a result, stand-alone YAG:Ce³⁺ nanospheres with an amorphous aluminum oxide layer shell were synthesized while maintaining monodispersity with an average particle diameter of about 33 nm. These nanospheres had a dense structure and smooth surface with relatively good crystallinity after annealing at 1075 °C. They absorbed light efficiently in the visible region of 400–500 nm, and showed a single broadband emission peak at 536 nm with a luminescence quantum efficiency (QE) of 33% and relatively good photostability.