The relationship between the growth rate of the hydroxyapatite (0001) face and bulk supersaturation of a simulated body fluid was measured by real-time Moire phase shift interferometry. It was found that the (0001) face grew in the multiple two-dimensional nucleation mode, from surface observation by atomic force microscopy, and the growth rate data were fitted by the theoretical equation of multiple two-dimensional nucleation. The edge free energy of an island nucleated on the (0001) face, the most important parameter for two-dimensional nucleation, could be directly estimated as gamma = 3.3kT, which was almost the same order as that on the (110) or (101) face of a lysozyme protein crystal.