PVC crosslinking is the most effective way to improve mechanical properties of rigid or flexible PVC at high temperatures, but at the same time the thermal stability of PVC may be significantly reduced. In the present work, the thermal stability of rigid crosslinked PVC has been evaluated by studying the pyrolysis behaviour. Crosslinked PVC was obtained by processing, under industrial type conditions, of formulations obtained from several concentrations of two different crosslinking systems: peroxide/TMPTMA and aminosilane. While the thermal behaviour in inert atmosphere has revealed appreciable modifications in the dehydrochlorination process for silane crosslinked PVC, differences in peroxide crosslinked samples mainly concern the degradation of the co-crosslinking agent (TMPTMA: trimethylpropane trimethacrylate), which decomposition is delayed as crosslinking advances. Furthermore, experimental data have been correlated by using a relative low number of parameter (considering the number of curves fitted and the complexity of the phenomena involved) in a simple model, which assumes the existence in samples of crosslinked and uncrosslinked phases. Kinetic analysis have revealed that the dehydrochlorination process in peroxide crosslinked PVC is practically unaffected. This, together with the observed enhancement of mechanical properties, suggests that peroxide/crosslinkable monomer systems are suitable for crosslinking rigid PVC.