The　nonlinear　dynamic　responses　of　functionally　graded　material　(FGM)　rectangular　plates　under　combined　transverse　and　in-plane　excitations　were　investigated　under　different　internal　resonances.　The　material　properties　were　assumed　to　be　temperature-dependent　and　varying　along　the　thickness　direction.　The　thermal　effect　due　to　one-dimensional　temperature　gradient　was　included　in　the　analysis.　The　governing　equations　of　motion　for　FGM　rectangular　plates　were　derived　by　using　Reddy＇s　third-order　plate　theory　and　Hamilton＇s　principle.　The　Galerkin＇s　approach　was　utilized　to　reduce　the　governing　differential　equations　to　a　two-degrees-of-freedom　nonlinear　system　including　quadratic　and　cubic　nonlinear　terms,　which　were　then　solved　numerically　by　using　4-th　order　Runge-Kutta　algorithm.　The　resonant　cases　considered　herein　are　1:1,　1:2　and　1:3　internal　resonances　and　principal　parametric　resonance-1/2　subharmonic　resonance.　The　effects　of　plate　geometry　parameters,　in-plane　excitations　and　temperature　field　on　the　internal　resonance　relationship　and　nonlinear　dynamic　response　of　FGM　plates　were　studied.　Numerical　results　show　that　in　the　cases　of　1:2　internal　resonance　and　principal　parametric　resonance-1/2　subharmonic　resonance,　the　vibration　amplitude　of　the　plate　center　is　much　greater　than　in　the　other　two　cases　of　the　internal　resonances.