YAG:Ce precursors were synthesized via a homogeneous precipitation method with the addition of different molecular mass of PEG (PEG 6000 and PEG 10000) used as dispersant. The FT-IR spectra show that no significant difference is found between the precursors. SEM images indicate that the size of the primary particles with PEG is much smaller than that of the sample without PEG. Confirmed by the DSC traces and X-ray diffraction (XRD), the crystallization of YAG is a one-step process without any intermediate phase. The crystallization of YAG is significantly promoted and the oxidation of Ce3+ is inhibited by addition of PEG, which enhances the luminescent properties of YAG:Ce phosphor.