Very stable dicalcium phosphate(DCP) against NaF was prepared by heat treatment at 200°C with adding Mg compound and condensed phosphate to DCP anhydrous. The crystal form and surface morphology of the improved DCP anhydrous were compared to that of standard DCP anhydrous. These characteristics were the same as those of standard DCP anhydrous. Although our surface modification technology was considered to keep the original characteristics of standard DCP anhydrous, even the crushed sample by an agate mortar showed a sufficient stability against NaF.