The long afterglow SrAl2O4:Dy,Eu phosphor is liable to hydrolyze in water with deterioration of the luminescent property. SrAl2O4:Dy,Eu phosphors were therefore heated at 60-90℃ in TEOS sol to form a surface gel and then heat-treated at 400℃ to obtain SiO2 coated phosphors. Observation by Transmission Electron Microscope (TEM) and X-ray photoelectron spectroscopy (XPS) shows that a thin silica film forms on the surface of the phosphors. The coating procedure can be illustrated by a four-step process and the transparent silica film can suppress the hydrolysis process, so that the luminescent properties of the phosphors are unimpaired or even better.