This research is directed toward understanding the effect of nanoparticle attributes and polymer morphology on the properties of the nanocomposites with analogous nanoparticle chemistry. In order to develop this understanding, polymer nanocomposites containing calcium phosphate nanoparticles of different specific surface areas and shapes were fabricated and characterized through thermal and thermomechanical techniques. Nanoparticles were synthesized using reverse microemulsion technique. For nanocomposites with different surface area particles, the mobility of amorphous polymer chains was restricted significantly by the presence of particles with an interphase network morphology at higher loadings. Composites fabricated with different crystallinity matrices showed that the dispersion characteristics and reinforcement behavior of nanoparticles were governed by the amount of amorphous polymer fraction available. The study conducted on the effect of nanoparticle shape with near-spherical and nanofiber nanoparticles illustrated that the crystallization kinetics and the final microstructure of the composites was a function of shape of the nanoparticles. The results of this research indicate that nanoparticle geometry and matrix morphology are important parameters to be considered in designing and characterizing the structure-property relationship in polymer nanocomposites.