In　this　paper,　we　use　the　asymptotic　perturbation　method　based　on　the　Fourier　expansion　and　the　temporal　rescaling　to　investigate　the　nonlinear　oscillations　and　chaotic　dynamics　of　a　simply　supported　rectangular　plate　made　of　functionally　graded　materials　(FGMs)　subjected　to　a　through-thickness　temperature　field　together　with　parametric　and　external　excitations.　Material　properties　are　assumed　to　be　temperature-dependent.　Based　on　the　Reddy＇s　third-order　plate　theory,　the　governing　equations　of　motion　for　the　plate　are　derived　using　the　Hamilton＇s　principle.　The　Galerkin　procedure　is　employed　to　obtain　a　two-degree-of-freedom　nonlinear　system　including　the　quadratic　and　cubic　nonlinear　terms.　The　resonant　case　considered　here　is　1:2　internal　resonance,　principal　parametric　resonance-1/2　subharmonic　resonance.　Based　on　the　averaged　equation　in　polar　coordinate　form,　the　stability　of　steady　state　solutions　is　analyzed.　The　phase　portrait,　waveform　and　Poincar,　map　are　used　to　analyze　the　periodic　and　chaotic　motions　of　the　FGM　rectangular　plate.　It　is　found　that　the　FGM　rectangular　plate　exhibits　the　chaotic　motions　under　certain　circumstances.　It　is　seen　that　the　nonlinear　dynamic　responses　of　the　FGM　rectangular　plate　are　more　sensitive　to　transverse　excitation.　The　excitation　force　can　be　used　as　a　controlling　factor　which　can　change　the　response　of　the　FGM　rectangular　plate　from　periodic　motion　to　the　chaotic　motion.