Nanocomposites of polyvinylidene fluoride/polymethyl methacrylate (PVDF/PMMA) blend and mechanically activated barium titanate (BaTiO₃) particles were prepared by melt mixing. Modification of filler by means of mechanical activation has a profound effect on the crystallization of PVDF in the blend matrix. Raman analysis showed that the modified BaTiO₃ particles, due to higher specific surfaces, induce, predominantly, the crystallization of the electrically active β-phase of PVDF, while the initial micron size particles induce the formation of the most common but non-polar α-crystal form. The introduction of activated particles reduces the overall crystallinity but slightly affects the crystallization and melting temperatures of the matrix. Dielectric spectroscopy revealed that at fixed filler content the dielectric constant of the blend increases with decreasing of the particle size (increasing of the activation time). A similar trend was observed for the storage moduli in dynamic mechanical analysis; the stiffness of the composite was higher when mechanically activated particles were used.