Ultrasonic　guided　wave　is　one　of　the　most　popular　techniques　in　analyzing　the　propagation　of　elastic　guided　wave.　The　goal　of　this　paper　is　to　investigate　the　propagation　of　elastic　waves　in　the　isotropic　bar　with　noncircle　cross　section.　Dispersion　curves　that　describe　the　relationship　between　the　wave　number　and　frequency　provide　the　fundamental　information　to　describe　the　propagation　of　elastic　waves　through　a　structure.　On　the　basis　of　the　FE　(Finite　Element)　model　and　their　translational　invariance,　a　linear　algebraic　system　of　equations　is　obtained.　By　using　numerical　methods,　fundamental　date　is　solved　for　the　structures　with　the　noncircle　cross　section.　By　comparing　with　the　dispersion　curves　of　the　cylindrical　waveguides,　many　differences　can　be　observed.　A　far　more　complex　behavior　is　observed　resulting　from　the　change　for　the　geometry　parameter.　Such　fundamental　information　plays　an　important　role　in　applying　ultrasonic　guided　waves　to　NDT　for　structures　with　noncircle　cross　section.　©　2015　Taylor　&　Francis　Group,　London.