Biominerals exist in scale, fin and tooth of seawater Lateolabrax Japonicus. In this paper, the crystallographic characteristics of the inorganic mineral phase existing in scale, tooth and bone (fin, sphenoid, backbone) from seawater Lateolabrax Japonicus were investigated by means of Xray micro diffractometry (XRMD), transmission electron microscopy(TEM)，environmental scanning microscopy (ESEM) and energy dispersive spectrometry (EDS). XRMD can well help to obtain valuable structure information by ways of insitu and nondestruction measurements, and hence it is a more suitable method than powder diffraction in biomineral studies. The results show that the crystal phase in these hard tissues is sole hydroxylapatite (HAP).The chemical composition characteristics of HAP in hard tissues is lack of Ca and rich in P except sphenoid. Refined lattice parameters of HAP show that in scale: a=09421 09461nm and c=06844 06907nm and the closer to the scale base, the value of lattice parameters is closer to that of the scale base, in bone: a=09438 09492nm and c=06873 06887nm and in tooth: a=09470nm and c=06883nm. The coherent domain sizes calculated from the Scherrer equation are Dscale=〖JP2〗94~141nm, Dbone=162~183nm and Dtooth= 151nm. From bone to tooth to scale it shows a crystallinity sequence from good to poor. Xray diffraction patterns and textural index 〖JP〗R values indicate that all HAPs in hard tissues of Lateolabrax Japonicus have a preferring orientation along crystallographic c axis. The crystallographic charateristics of biominerals (grain size, crystallinity and preferring orientation) are designed by tissue function and controlled by organic matrix to provide good mechanical performance.