Ferroelectric-paraelectric (F-P) phase transition behavior of P(VDF-TrFE) 80/20 mol% under high-energy electron irradiation is studied based on X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermally stimulated depolarization current (TSDC). Irradiation causes reduction of the polar domain size and expansion of non-polar crystalline size from all-trans to trans-gauche conformation in nanometer range, showing the coexistence of polar and non-polar phase. Both the Curie temperature T-c and melting temperature T-m decrease and exceptional endothermic peaks appear during the heating process in DSC thermograms, indicating the non-polar phase embedded in the crystalline region for the irradiated copolymers. The effect of non-polar phase is also observed in TSDC measurement, which shows prominent current change with irradiation dose in the low temperature range. It is believed that the coexistence of the non-polar and polar phases leads to the change of phase transition behavior in the irradiated P(VDF-TrFE) copolymers with a high VDF content. (C) 2003 Elsevier Science B.V. All rights reserved.