The deformation and fracture mechanism during uniaxial tension under controlled strain rates are investigated for extruded poly(vinylidene fluoride) (PVDF) polymer films at room temperature. It was found that both the longitudinal and transversal film-samples exhibited pronounced strain rate effect, that is, the yield stress increases while the fracture strain decreases with the increasing of strain rates. For the longitudinal film samples, phase transformation from the nonpolar alpha-phase to the polar beta-phase occurs during the uniaxial tension, and the extent of the phase transformation enhances when the strain rate decreases. For the transversal film samples, no phase transformation was detected in all tested strain rates. By combining the stress-strain behavior and the X-ray results, it can be inferred that the conformational change from alpha to beta phase during uniaxial tension contributes to the higher fracture strain of the longitudinal films than that of the transversal films. (c) 2006 Wiley Periodicals, Inc.