The effect of silylation of microfibrillated cellulose (MFC) surfaces on β‐phase formation in poly(vinylidene difluoride) (PVDF) and the resulting viscoelastic and dielectric performance of MFC‐PVDF composites is investigated. Two different organosilanes, namely aminated (A) and fluorinated (F), were used. Composites of PVDF and MFC at concentrations up to 10 wt%, both untreated and silylated, were prepared by solvent casting. The two different surface modifications did not markedly change the melting and crystallization enthalpy of the polymer. However, only A‐MFC was found to promote β‐phase compared to the untreated MFC and the F‐MFC, which was attributed to the formation of hydrogen bonds at the interface between the amine groups of A‐MFC and the fluorine groups of PVDF. The elastic modulus and the permittivity of all composites increased with the amount of MFC up to a maximum value, depending on the MFC modification, and then decreased. This effect was due to the formation of MFC aggregates and porosity, as further confirmed by a comparison of experimental moduli with a classical composite mechanical model. The highest elastic modulus and highest permittivity were obtained for the untreated MFC and A‐MFC composites with 5 and 1 wt%.