Various bionanocomposites were prepared by dispersing fumed Silica (SiO2) nanoparticles in biocompatible polymers like poly(vinyl pyrrolidone) (PVP), chitosan (Chi), or poly(vinyl alcohol) (PVA). For the bionanocomposites preparation, a solvent evaporation method was followed. SEM micrographs verified fine dispersion of silica nanoparticles in all used polymer matrices of composites with low silica content. Sufficient interactions between the functional groups of the polymers and the surface hydroxyl groups of SiO2 were revealed by FTIR measurements. These interactions favored fine dispersion of silica. Mechanical properties such as tensile strength and Young's modulus substantially increased with increasing the silica content in the bionanocomposites. Thermogravimetric analysis (TGA) showed that the polymer matrices were stabilized against thermal decomposition with the addition of fumed silica due to shielding effect, because for all bionanocomposites the temperature, corresponding to the maximum decomposition rate, progressively shifted to higher values with increasing the silica content. Finally, dynamic thermomechanical analysis (DMA) tests showed that for Chi/SiO2 and PVA/SiO2 nanocomposites the temperature of P-relaxation observed in tan delta curves, corresponding to the glass transition temperature T-g, shifted to higher values with increasing the SiO2 content. This fact indicates that because of the reported interactions, a nanoparticle/matrix interphase was formed in the surroundings of the filler, where the macromolecules showed limited segmental mobility. (C) 2008 Wiley Periodicals, Inc.