The paper describes the influence of barium titanate BaTiO3 used as a filler in impregnating epoxy resin on electrical parameters of obtained material. The results of computer simulation of electric field intensity distribution in area of 220 kV ac composite insulator show that in order to reduce the maximum value of this field it is necessary to use the rod with the highest possible permittivity. It was assumed that the increase of rod permittivity is possible by doping the epoxy resin, being one of glass-epoxy rod components, with a filler having high permittivity. Barium titanate BaTiO3 in micro- and nanograins was used as a filler. Presumably, such a change in material structure, may negatively influence other electrical parameters of the material, important in composite insulators construction. In order to check the filler dispersion in epoxy matrix, microscopic observations of fractions of the obtained materials were performed. In a wide range of frequencies, the permittivity and volume resistivity of the materials were determined. The inception voltage of partial discharges on surface of materials was determined by the electric, acoustic and antenna methods.