Surface modification on nanoparticle fillers with organic groups is important to improve the performance of ceramic/polymer nanocomposites. Due to the small coverage level of carboxylic acids on the nanoparticle surface, studies on the use of carboxylic acids as a surface modifier for ceramic nanoparticles have been rarely reported. However, there is no study that proves that a small amount of modifier on the surface of nanoparticles cannot adequately improve the dispersion as well as the compatibility of nanoparticles with the matrix. Herein, we used three carboxylic acids to treat the surface of BaTiO₃ (BT) nanoparticles and adjusted the coverage level of the modifiers on the surface of BT nanoparticles through different ways. The nanocomposite films synthesized from the modified BT nanoparticles dispersed in the poly(vinylidene fluoride) (PVDF) polymer matrix were analyzed by dielectric spectroscopy, breakdown strength, leakage currents, and D–E loop measurements. The results show that the molecule dipole moment and polarizability of the modifier greatly influence the permittivity of the nanocomposites as the surface coverage level of the modifiers increases. Due to many influential factors, changes in the breakdown strength of the nanocomposites show diversity for three modifiers as the modifier content increases. For the nanocomposites applied in energy storage, the optimal content of the modifier on the surface of the nanoparticles needs to be determined by combining various properties of the nanocomposites.