Thermal decomposition products of polyamide-6,6 (PA-6,6) and acrylonitrile-butadiene-styrene copolymer(ABS) have been converted over Y zeolites at above the temperature of thermal decomposition of these polymers. On-line pyrolysis-gas chromatography/mass spectrometric (Py-GC/MS) analysis revealed the nature of chemical reactions of the pyrolysis gas and oil components taking place over protonic and sodium Y zeolite. Selected TG-MS ion curves of polymer and zeolite mixtures indicated the changes due to the catalytic conversion of the thermally produced products in to compounds of high volatility. The experimental results demonstrate that protonic Y zeolite (HUSY and NH4Y) denitrogenate the pyrolysis oil components and transform the hydrocarbon part of their molecules into aromatic compounds. Over sodium Y zeolite (NaY) pyrolysis product molecules of low volatility are cracked to gases and to compounds of gasoline volatility, but no denitrogenation occur. The aromatizing and hydrogenating activity of NaY zeolite is considerably lower, than that of protonic Y zeolites. (C) 2008 Elsevier B.V. All rights reserved.