Poly(vinylidene fluoride)(PVDF)/Na+-MMT composites have been successfully prepared utilizing sodium montmorillonite (Na+-MMT) via N,N-dimethylformamide (DMF) solution mixing. The dispersion of Na+-MMT layers in composites were investigated by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The effect of adding Na+-MMT on crystallization behavior of PVDF was specifically studied. The beta-crystalline nucleation effect of Na+-MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na+-MMT layers in DMF solution was confirmed by UV-Vis absorbency. The effect of adding Na+-MMT on rheological and electrical properties of PVDF/Na+-MMT composites were also determined. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903-911, 2009