Abstract: The dispersion characteristics of a class of closed dielectric waveguide areinvestigated by the method which combines the building-block approach of multimode network theory with rigorous mode matching procedure. Several numerical examples for different guiding structures have been given by the approach. The same structures are also analyzed with the finite element method and the EDC method for comparison. The calculations show that the present approach yields as highly accurate results as the finite element method while almost retaining the simplicity of the EDC method, and justify the utility of the present method.