A new approach to dielectric material characterization with a vector network analyzer is presented. As the characteristic impedance (Z0) of a stripline transmission line can be accurately determined by measuring the two-port scattering parameters in the frequency range of interest, the dielectric constant of the insulation material that consists as part of the stripline configuration is then obtained by a relationship to the characteristic impedance. The dielectric loss (or loss tangent) can be determined by measuring the return loss and the insertion loss of the stripline. The validity of the technique is demonstrated for well-characterized dielectric materials such as Teflon-based and other composite laminates. The technique is then applied to integrated circuit (IC) molding compounds as-processed.