The β-relaxadon of PEN in Thermally Stimulated Current (TSC) is firstly reported in the present paper. The effects of the variation of electrode materials and polarization field strength on TSC peaks indicate that the β-relaxation is due to the dipolar contribution. The effects of the crystallinity variation on the 3 peak current and on the activation energy of the β-relaxation further indicate that the molecular origin of the β-relaxation is the local segmental motion of PEN chain in the amorphous region.