Abstract: The formation of laminated thin plate-shaped hydroxyapatite (HAP) nanocrystals from organically modifided plate-shaped octacalcium phosphate (OCP) under hydrothermal condition which are performed at 180℃ for 3h with pH of solution adjusted to 5.5, further it incorporated succinate ion having Ca/P molar ratio is expected to be 1.56±0.02. The morphological observation of crystals have been characterized by XRD, SEM and other using patterns. Since, the HAP crystal system is hexagonally and its crystallite size in the direction of various (a,b,c) axes depending on the plate-shaped HAP crystals thickness, where their size as perpendicular to the (100) plane is calculated by using of Scherrer equation D100 = Kλ/(β cosθ).