In this study, a new optically active poly(ester-imide) (PEI) was synthesized from the polymerization reaction of N,N'-(pyromellitoyl)-bis-L-phenylalanine diacid with 4,4'-thiobis(2-tert-butyl-5-methylphenol) using tosyl chloride, pyridine and N,N-dimethyl formamide as a condensing agent. The obtained polymer and inorganic metal oxide bionanocomposites composed of poly(ester-imide)/titanium dioxide were synthesized through ultrasonic irradiation. The formation of PEI was confirmed by H-1 NMR, fourier transform IR spectroscopy (FT-IR), specific rotation and elemental analysis. The resulting bionanocomPosites were characterized by FT-IR, powder X-ray diffraction (XRD), atomic force microscopy)AFM(, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The TEM, SEM and FE-SEM results indicated that the nanoparticles were dispersed homogeneously in PEI matrix on nanoscale. TGA confirmed that the heat stability of the nanocomposite was improved in the presence of TiO2 nanoparticles. (C) 2010 Elsevier Ltd. All rights reserved.