A method for preparing a rare earth activated alkaline earth metal fluorohalide stimulable phosphor represented by formula (Ba1−xM2x)FBryI1−y:aM1, bLn, cO is discloded, comprising the steps of (a) preparing an aqueous mother liquor containing BaX2 of not less than 2.0 mol/l and a halide of Ln, (b) adding an aqueous solution containing an inorganic fluoride of not less than 5 mol/l to the mother liquor while maintaining a temperature of at least 50° C. to form a crystalline precipitate of a precursor of the stimulable phosphor, (c) separating the precipitate of the precursor from the mother liquor, and (d) calcining the separated precipitate.