In this work, thermal degradation behavior polystyrene/organoclay nanocomposites containing tribromophenol end-capped brominated epoxy oligomer, (BE) with or without Sb2O3 were investigated systematically via direct pyrolysis mass spectrometry. Incorporation of organically modified montmorillonite into polystyrene, (PS) matrix not only increased thermal stability but also the probability of radical recombination, disproportionation and carbonization reactions causing increase in the char yield. Exfoliation of organoclay in BE phase of PS-BE matrix affected the extent of radical coupling and disproportionation reactions between the thermal degradation products of PS and organic modifier. In addition, the evolution of BE based products was hindered partly and the attacks of HBr to epoxy units generating H2O became more efficient. During the pyrolysis of polystyrene/organoclay nanocomposite involving both BE and Sb2O3, the relative yields diagnostic products of both oxybromides and bromides of antimony were increased significantly in the temperature region where PS decomposition took place which in turn increased the efficiency of radical scavenging and reduced peak heat release rate while increasing limiting oxygen index. (C) 2016 Elsevier B.V. All rights reserved.