This present paper is a study of the dielectric behavior of carbon black-epoxy resin composites at the microwave frequencies 9.5 and 35 GHz. The results of this research have shown that the complex propagation constant gamma(g) for these mediums depends on the frequency F, on the volume concentration phi of the conducting medium, and on the particle size. Numerical simulations allow us to fit the dependence of the measures upon the sample thickness, but we have to assign dielectric and diamagnetic properties of the heterogeneous medium. The permittivity and the permeability depend on the particle concentration, and the real part of the permeability is always smaller than unity.