In　this　paper,　an　analysis　on　nonlinear　dynamics　behavior　of　a　simply　supported　orthotropic　functionally　graded　materials　rectangular　plate　in　thermal　environment　with　parametric　and　external　excitations　is　presented.　Material　properties　are　assumed　to　be　temperature-dependent.　By　the　Reddy＇s　third-order　plate　theory,　the　Hamilton＇s　principle　and　the　Galerkin　procedure,　the　three-degree-of-freedom　nonlinear　the　governing　equations　of　motion　for　the　orthotropic　FGM　rectangular　plate　are　derived　The　resonant　case　considered　here　is　1:2:4　internal　resonance,　principal　parametric　resonance-1/2　subharmonic　resonance.　Based　on　the　averaged　equation　obtained　by　the　method　of　multiple　scales,　the　phase　portrait,　waveform　and　Poincare　map　are　applied　to　analyze　the　periodic　and　chaotic　motions.　Under　certain　conditions　the　chaotic　motions　of　the　orthotropic　FGM　plates　are　found.