Radiation crosslinked polytetrafluoroethylene (XPTFE) has many properties compared to non-crosslinked PTFE, such as excellent friction resistance, better transparency and lower melting point, which may be applied for high temperature processing or sintering. In this paper the thermal stability of a series of XPTFE samples thermally treated over 340℃－400℃ in airwas investigated. It was found that melting point and crystallization temperature of XPTFE increased, meanwhile morphology deformation and decrement of molecular weight was also observed after thermal treatment. It indicates that the thermal stability of XPTFE becomes poorer along with the in-crement of the irradiation crosslinking dose. It can be suggested that the optimal dose for preparing XPTFE should be less than 100 kGy as the thermal stability of XPTFE is dependent on the crosslingking dose.Cited