The　chaotic　behavior　of　a　flexible　cantilever　beam　subjected　to　harmonic　base　in-plane　excitation　is　investigated　in　this　paper.　The　excitation　frequencies　and　amplitudes　which　can　lead　to　chaotic　vibration　of　the　beam　are　obtained.　The　experimental　results　indicate　that　chaotic　vibration　can　occurs　at　two　excitation　frequencies　in　which　one　of　the　two　frequencies　is　twice　as　large　as　the　other　one.　However,　the　minimal　excitation　amplitudes　are　quite　different　at　the　two　excitation　frequencies,　and　the　vibration　responses　after　chaos　have　much　in　common.　©　2011　IEEE.