Poly(vinylidene fluoride) (PVDF)/montmorillonite (MMT) composite with different MMT contents were prepared by solutions-casting method. The effects of MMT on crystalline structure, morphology, dielectric property, piezoelectric property and phase transformation mechanism were studied. The results showed that acted as effective nucleation agents, the orientation of MMT were almost parallel to the surface of the film. The beta phase in the PVDF matrix was increased and the alpha phase was decreased. Relative dielectric constant and loss of the composite were increased with the increasing of MMT. The d33 was also increased with MMT, which reached a maximum (5.8pC/N) with 2.0 wt % MMT. The mechanisms of changes in phase transformation and piezoelectric property were proposed based on experiment results. (c) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012