Poly(vinylidene fluoride)/Microcrystalline cellulose (MCC) nanocomposites were prepared by ultrasonic treatment and magnetic stir. Poly(vinylidene fluoride)-graft-maleic anhydride (PVDF-g-MAH) was added to promote matrix–filler compatibility. Transmission electron microscopy (TEM) results showed that the diameter of the MCC was decreased to several tens nanometers by the treatment of ultrasonic and magnetic stir. The results of differential scanning calorimetry (DSC) showed that the peak crystallisation temperatures (Tc) and the crystallisation enthalpy ΔHc increased with the addition of MCC, and the melting enthalpy ΔHm increased. With the addition of the compatibilizer (PVDF-g-MAH), peak crystallisation temperatures increased further, while without further increase of the ΔHc. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) showed that the addition of MCC induced β-phase PVDF, and the addition of PVDF-g-MAH can induce more β-phase PVDF. Mechanical properties of the nanocomposites were evaluated and the results showed that the addition of MCC did not increase the Young’s modulus, while the tensile strength and elongation at break decreased.