The present paper reports high frequency microwave characterization of both the single- and multi walled carbon nanotubes and quantifying microwave absorption through the measurements of S parameter. The dielectric properties for these nanostructured carbon materials are measured using the rectangular waveguide technique and are determined in the frequency regime ranging 8-40 GHz. The data is represented in terms of both the real and imaginary parts of permittivity and permeability. These results represents a milestone in such measurements for nanoscale cylindrical conductors i.e. carbon nanotube structures which serves as a model example and it covers a wide frequency range using an efficient, non-invasive and highly accurate technique that is ideal for high frequency characterization for a variety of nanoscale materials.