PAN undergoes chemical decomposition in stages on thermal treatment. In the literature, several mechanisms were proposed for the degradation process. However, the decomposition pathway and the structural rearrangement of solid residue in relation to the loss of volatile products are not fully understood. The degradation process has therefore received further attention in this work by employing a combination of FT-IR, high-resolution solid-state C-13-NMR, pyrolysis GC-MS, and microelemental analysis. These investigations have established that PAN decomposes to gaseous and volatile products over a range of temperatures (150-590 degrees C) with concurrent stabilization of the structure of residual matter occurring on a parallel course. While linear polymerization of nitrile group is the principal reaction in the decomposition process, cyclization followed by extended conjugation is the notable exothermic process. No evidence has been obtained for the formation of oxygen-containing chromophores either as intermediates or as part of the chemical structure of the residue. Temperature sensitivity of oligomer formation has been established through pyrolysis-GC-MS studies. The overall decomposition profile of PAN has thus been established.