Nano particle hydroxyapatite was synthesized based on wet chemical precipitation method. The precipitated hydroxyapatite powders are characterized using Inductively Coupled Plasma Spectroscopy(ICP), FT-IR spectroscopy, X-ray diffraction(XRD), transmission electron microscopy(TEM), and electron diffraction(ED). Hydroxyapatite with different mean nano particle sizes in the range of 20~160 nm was prepared. Particle sizes were mainly determined by reaction temperature. Influences of degree of supersaturation, stirring intensity and reaction temperature were analyzed based on crystallization process analysis.