Polyvinylidene fluoride (PVDF) based nanocomposites with graphene and ionic liquid-modified graphene (denoted as GIL) as fillers, were fabricated using solution-cast method and their dielectric properties were carefully characterized. The Raman spectroscopy showed that the ionic liquid and the graphene exhibit the physical cation-π interaction. Ionic liquid can improve the dispersibility of graphene in PVDF matrix by morphology characterization. The percolation thresholds were determined to be 1.86 vol % for PVDF/GIL composites and 0.67 vol % for PVDF/Graphene composites, respectively. Compared with PVDF/Graphene composites, the PVDF/GIL composites exhibited higher dielectric permittivity that originates from the polar β crystals of PVDF and a remarkable Maxwell–Wagner–Sillars (MWS) effect between PVDF and GIL, and the nonconducting organic segments of the ionic liquid can support the low loss tangent and low conductivity in the PVDF/GIL composites.