Broadband dielectric spectroscopy was employed to study polymer nanocomposites based on PA12 filled with of nanosized chromium(III) oxide. The experimental dielectric data were analyzed within the formalisms of complex permittivity and electric modulus. Three relaxation processes and Maxwell-Wagner-Sillars (MWS) interfacial polarizations were observed. It was found that presehce of nanosized amphoteric chromium(III) oxide leads to softening of polyamide matrix that manifested in decrease of the activation energy of the alpha- and 13 beta-relaxation processes and glass transition temperatures. The softening of polymer matrix is the reason of the decrease of mechanical strength of polymer nanocomposites as compared with neat PA12. (C) 2016 Elsevier B.V. All rights reserved.