Abstract: In this paper, starting from solving eigenvalue problem of wavegurdes filled with inhomogeneous dielectrics, fin-line dispersion is calculated by means of the finite element method. As a result of considering the effect caused by the fin thickness on dispersion, the results obtained by other methods may be modified. The dispersion characteristics obtained by unified program for fin-line, ridged waveguide and slab-loaded waveguide are in good agreement with results obtained by other methods. Practical measurements of dispersion shaw an agreement between computed results with fin thickness to be considered and experiments, thus justify the discribed method.