Tungsten oxide hydrate (WO₃·H₂O) nanoparticles (NPs) have been prepared by simple hydrazine hydrate reduction. X-ray diffraction, UV-Visible spectroscopy and field emission electron scanning microscopy confirm the formation of phase pure orthorhombic WO₃·H₂O NPs. Thereafter, poly(vinylidene fluoride) (PVDF) thin films doped with different amounts of WO₃·H₂O NPs (1–15 mass%) have been prepared via a simple solution-casting method to verify the role of the NPs on the enhancement of electroactive β phase crystallization and dielectric properties of WO₃·H₂O NP–PVDF thin films. The interface between the NPs and the polymer matrix takes a vital role in improving β phase nucleation and dielectric properties of the WO₃·H₂O NP modified PVDF thin films. Strong electrostatic or ion–dipole interaction between the negatively charged NP surfaces and –CH₂ dipoles of the polymer matrix at the interface effectively improves the electroactive β phase nucleation and dielectric properties of the nanocomposite thin films.