In　this　paper,　we　use　the　asymptotic　perturbation　method　to　investigate　the　nonlinear　oscillation　and　chaotic　dynamic　behavior　of　a　simply　supported　rectangular　plate　made　of　functionally　graded　materials　(FGMs).　We　assume　that　the　plate　is　made　from　a　mixture　of　ceramics　and　metals　with　continuously　varying　compositional　profile　such　that　the　top　surface　of　the　plate　is　ceramic　rich,　whereas　the　bottom　surface　is　metal　rich.　The　equations　motion　of　the　FGM　plate　with　two-degree-of-freedom　under　combined　parametrical　and　external　excitations　are　obtained　by　using　Galerkin＇s　method.　Based　on　the　averaged　equation　obtained　by　the　asymptotic　perturbation　method,　the　phase　portrait　and　waveform　are　used　to　analyze　the　periodic　and　chaotic　motions.　It　is　found　that　the　FGM　plate　exhibits　chaotic　motions　under　certain　circumstances.