The　nonlinear　dynamic　response　of　functionally　graded　rectangular　plates　under　combined　transverse　and　in-plane　excitations　is　investigated　under　the　conditions　of　1　:　1,　1　:　2　and　1　:　3　internal　resonance.　The　material　properties　are　assumed　to　be　temperature-dependent　and　vary　along　the　thickness　direction.　The　thermal　effect　due　to　one-dimensional　temperature　gradient　is　included　in　the　analysis.　The　governing　equations　of　motion　for　FGM　rectangular　plates　are　derived　by　using　Reddy＇s　third-order　plate　theory　and　Hamilton＇s　principle.　Galerkin＇s　approach　is　utilized　to　reduce　the　governing　differential　equations　to　a　two-degree-of-freedom　nonlinear　system　including　quadratic　and　cubic　nonlinear　terms,　which　are　then　solved　numerically　by　using　4th-order　Runge-Kutta　algorithm.　The　effects　of　in-plane　excitations　on　the　internal　resonance　relationship　and　nonlinear　dynamic　response　of　FGM　plates　are　studied.