Bone is in important material to study due to its exceptional mechanical propeties and relevance with respect to hard tissue regeneration and repair. A significant effort Is been directed toward understanding the bone formation process and the production of synthetic bone, mimicking materials. Here, the formation and structural evolution Of calcium,phosphate,(CaP) was investigated in the presence of relatively high concentrations of calcium;. phosphate; and polyaspartic add (pAsp) using dynamic light scattering (DES) and cryo-transmission electron microscopy (cryo-TEM). The incipient CaP aggregates were comprised of spherical nanopartides (diameter approximate to 3-4 nm); they became preferentially aligned over time and eventually transformed into nanorods. The nanorods remained stable in suspension with no signs of further aggregation for at least four months. Detailed cryo-TEM suggested that the CaP nanorods formed through an oriented attachment mechanism These results show that the reaction concentration greatly influences the mechanism and final properties of CaP. Mechanistic insights gained froth this study will facilitate better design and fabrication of bioinspired materials.