In this paper, a new method of measurement of resistivity of thin films and dielectric constant of slabs using open-ended coaxial lines is introduced. The model used in our analysis is an open-ended coaxial line with a large conducting flange terminated by layered materials to be measured. The reflection coefficient of the principal (TEM) mode is calculated, and it is found to be dependent on the thickness and the dielectric properties of the layered materials as expected. The admittance of the coaxial probe Y, is equivalent to a conductance G, for high conductive thin films, and it is also found to be proportional to the product of the thickness and the conductivity of the thin film. Each parameter may be readily calculated from the measured Y, values if one of them is known. The same method is used to find the dielectric constant of a single dielectric slab from the measured Y, values of the probe and the thickness of the slab. Experimental results of resistive thin films (several tens of ohms per square) measured over a wide frequency band (up to 20 GHz) are in agreement with commercial nominal values, and the proposed method of measurement and field analysis is thus justified. This wide-band method of measurement has the advantage of facilitating the preparation of the test samples.