Thermal processing at various temperatures has been used to fabricate poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-co-TrFE)] films with varied crystalline properties in an attempt to improve their piezoelectric properties. Although the dielectric constant of the films annealed at higher temperature is smaller than that of cooled and quenched ones, it has been shown that the annealed films possess larger crystallinity and stacked lamellar crystal grain size. The ferroelectric domains deriving from crystal region in all the samples are effectively improved by hot polarization. As a result, the remnant polarizations (Pr) and coercive electric field (Ec) of the corresponding films are improved at a low frequency due to the response of dipoles in crystal phase, and the largest piezoelectric constant in the longitudinal thickness mode (d33=-25 pC/N) is obtained in an annealed copolymer film. The results illustrate improving the crystal structure of P(VDF-co-TrFE) is an effective way to realize high electromechanical properties, which provides broadly applied scenery for this kind of copolymer in piezoelectric components. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012