An　analysis　on　the　nonlinear　dynamics　of　a　simply　supported　functionally　graded　materials　(FGMs)　rectangular　plate　subjected　to　the　transversal　and　in-plane　excitations　is　presented　in　a　thermal　environment　for　the　first　time.　Material　properties　are　assumed　to　be　temperature　dependent.　Based　on　Reddy＇s　third-order　plate　theory,　the　nonlinear　governing　equations　of　motion　for　the　FGM　plates　are　derived　using　Hamilton＇s　principle.　Galerkin＇s　method　is　utilized　to　discretize　the　governing　partial　equations　to　a　two-degree-of-freedom　nonlinear　system　including　the　quadratic　and　cubic　nonlinear　terms　under　combined　parametric　and　external　excitations.　The　resonant　case　considered　here　is　1:1　internal　resonance　and　principal　parametric　resonance.　The　asymptotic　perturbation　method　is　utilized　to　obtain　four-dimensional　nonlinear　averaged　equation.　The　numerical　method　is　used　to　find　the　nonlinear　dynamic　responses　of　the　FGM　rectangular　plate.　It　was　found　that　periodic,　quasi-periodic　solutions　and　chaotic　motions　exist　for　the　FGM　rectangular　plates　under　certain　conditions.　It　is　believed　that　the　forcing　excitations　f(1)　and　f(2)　can　change　the　form　of　motions　for　the　FGM　rectangular　plate.　(c)　2007　Elsevier　Ltd.　All　rights　reserved.