The effect of shear or time of shearing - as exerted by different screw configurations - upon the nano hydroxyapatite (n-HA) dispersion, during the twin screw extrusion processing for the preparation of PA6-66/n-HA composites, was investigated. Three different screw configurations, designated as medium, high and very high shear, were used. A noticeable improvement in the n-HA dispersion, attributed to the increasing shear exerted upon the melt during mixing in the TSE, was observed. Crystallization and thermal behavior of n-HA reinforced PA6-66 composites were studied by X-Ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). An increase in the crystallization temperature, accompanied by a decrease in percent crystallinity with the addition of n-HA to the PA6-66 matrix was observed. That is, n-HA acted as a nucleating agent and enhanced the crystallization rate. In addition, it was observed that the n-HA promoted the occurrence of the Brill transition. The decomposition temperature increased with the addition of n-HA. The PA6-66/ n-HA nanocomposite was thereafter, immersed in simulated body fluid (SBF) and the generation of a new calcium phosphate layer on the nanocomposite surface was monitored by SEM, FTIR and Atomic Absorption. The Ca/P ratio in the forming apatite layer started at a low value, ca. 1.3, which corresponds to octacalcic phosphate, but increased with the immersion time to 1.6, which corresponds to carbonated apatite.