Composites of micronanosize BaTiO3 (BT) particles embedded into a polyvinylidene fluoride matrix were prepared. They were studied with respect to the effect of nanosize particles on microstructure and dielectric properties. The results show that the dielectric permittivity of composites with nanosize BT is close to the predicted values calculated at high concentration of fillers, if the interactions among BT fillers and between BT fillers and polymer are included. The enhanced dielectric permittivity mainly originates from a noticeably increasing phase interfaces in the composites, which brings out the strong interfacial polarization effect at low frequencies.