Orthogonal polynomial series approach has been used to analyze the guided wave propagation in structures for about 20 years. These structures have always one infinite dimension in the waveguiding direction and, sometimes a regular finite crosssection (axially infinite solid or hollow cylinder for instance) and mostly often an infinite cross-section (infinite flat plate or half-space for instance). This paper presents a double orthogonal polynomial approach to investigate guided wave propagation in structures with only one infinite dimension in the waveguiding direction and a finite but complicated cross-sectional geometries as, rectangular type, L-type, 工-type and 回-type cross-sections. Through a numerical comparison with results available in literature, the validity of the extended polynomial approach is illustrated for a specific geometry. The dispersion properties of guided waves in rods with complex cross-sections as mentioned above are discussed.