The promoting effect of phosvitin on the nucleation of hydroxyapatite (HAP) and the inhibitory effect of phosvitin on the transformation from amorphous calcium phosphate (ACP) to HAP were investigated. Atomic force microscopy observations showed that the nucleation of HAP on collagen substrate was greatly enhanced when the phosvitin was bound on the collagen surface. Nucleated crystals were uniformly distributed with a high nucleation rate on the collagen surface in the presence of phosvitin, while, in the absence of phosvitin, crystals nucleated slowly and were observed only at some particular area. Time-resolved static light scattering measurements revealed that the transformation from ACP to HAP was inhibited when free phosvitin was present in the calcium phosphate solutions. The transformation kinetics in the absence of phosvitin, which is a direct reconstruction of the inner ACP structure to HAP, was changed to heterogeneous growth of HAP on ACP with time.