A large transverse electrostrictive strain S1 with a high elastic strain energy density is observed along the drawing direction in the stretched poly(vinylidene fluoride–trifluorethylene) copolymer film under a proper electron irradiation treatment condition, which results in a ratio of ∣S1/S3∣ larger than 1 where S3 is the longitudinal strain. In contrast, unstretched films generate a relatively small transverse strain with a small ratio of ∣S1/S3∣ (∼0.25). Hence, in this copolymer system, the ratio of ∣S1/S3∣ can be varied over a broad range. In addition, a large volume strain, which amounts to about half of the longitudinal strain, is observed in the films investigated. © 1999 American Institute of Physics.