High resolution Brillouin spectroscopy (HRBS) backscattering elastic data in nanocomposites of ethylene-vinyl alcohol copolymer (EVOH) and TiO(2) nanoparticles present anomalous dependence with concentration, while Young's modulus and microhardness data show the expected behaviour. When performing HRBS with the 90A scattering geometry to asses the effective elastic constant, the expected behaviour for low concentration of TiO(2) nanoparticles is again obtained. This unusual disagreement can be solved assuming that the inclusion of TiO(2) nanoparticles induces anomalous refractive index behaviour at the applied laser wavelength for the different EVOH-TiO(2) nanocomposites. Comparison with experimental elastic and optical data obtained in isotactic-polypropylene-TiO(2) nanocomposites proves that EVOH-TiO(2) nanocomposites show an unusual optical behaviour at the laser wavelength, possibly due to a singular bonding between the EVOH polymer and the TiO(2) nanoparticles. (C) 2009 Elsevier Ltd. All rights reserved.