In order to develop effective final treatment system of waste plastics, thermal gasification characteristics of plastics compounds containing flame retardant were investigated. Polypropylene (PP) with flame retardant, which was composed by Al(OH)(3) or (NH4PO3)(m), was decomposed in an image furnace. Mass reduction during thermal decomposition was measured by an electric micro-balance. The gas components produced by the thermal decomposition were analyzed with a gas analyzer (MEXA 4000 FT, Horiba Ltd.). Soluble organic fraction (SOF) components in a condensable emission during the decomposition process were analyzed with a combustion type PM analyzer (MEXA 1370 PM, Horiba Ltd.). In addition, SOF and solid carbon in the remains after the thermal decomposition were also analyzed by the PM analyzer. The oxygen concentration was changed from 0% to 21% and the content of flame retardant was changed from 0% to 50%. It was found that thermal decomposition temperature increased with a decrease of oxygen concentration. Flame retardant had small effect on the thermal decomposition temperature. However, gas components produced by thermal decomposition were changed corresponding to the containing ratio of flame retardant. The mass of remains was also affected by the ratio of flame retardant. As for the PP with Al(OH)(3), it was considered that PP was completely decomposed and main component of the remains was Al2O3 produced by decomposition of Al(OH)(3) even if the surrounding temperature increased up to 900 K. As for the PP with (NH4PO3) gradual mass reductions continued after rapid mass reductions. The ratio of SOF and carbon contents in the remains after decomposition of PP with (NH4PO3)(n) were higher than the case of PP with Al(OH)(3.) (C) 2007 Elsevier Ltd. All rights reserved.