Three phase ceramic-metal-plastic (cermetplas) percolative nanocomposite films were prepared using polyimide, as the matrix to prepare the composite films. Silver nanoparticles with a mean particle size of about 41 nm were prepared and used as the metal phase. Nanocomposites of barium titanate (BaTiO3) particles in polyimide matrix, with silver as metallic inclusion, were formulated using effective medium theory and percolation theory. The concentration and frequency dependence of dielectric permittivity (epsilon) and loss tangent (tan delta) measurements were reported and discussed for cermetplas below the percolation threshold. Experimental results for cermetplas show that a epsilon of above 500 can be achieved below the percolation. (c) 2006 Wiley Periodicals, Inc.