The products obtained on degradation of poly(m-N,N-dimethylaminostyrene) in vacuo are described. The effects of molecular weight and pyrolysis temperature are discussed and compared with those observed for polystyrene under similar conditions. The liquid products of pyrolysis were separated and identified by gas–liquid chromatography using Kovats' retention index and by mass spectrometry. Product analysis revealed significant differences between the products of degradation of the two polymers, and mechanisms involving N-alkyl and N-aryl bond scission are proposed and discussed to account for this behavior. The degradation behavior of poly(m-N,N-dimethylaminostyrene) shows a marked molecular weight dependence. This is discussed in terms of the differences in the physical forms of the polymer produced on heating, namely, formation of a “melt” or retention of the original “fibrous” identity. Quantitative studies on the liquid fraction are also described and the behavior compared with results obtained on polystyrene.