Based on the parameters of scatter ing S11 and S21 measured exper imentally, an estimate of the dielectr ic permittivity of a mater ial is made inside a rectangular waveguide, using themodal analysis and integral relationships. A technique for to calculate the values of the dielectric permittivity complex in microwaves frequencies is presented, using the results of the measures, specifically of the transmission coefficient S21. It is elabor ated a graphic of mapping for fast and easy diagnosis of electric character istics of the studied biological sample.