An　analysis　on　the　nonlinear　forced　vibration　of　thermally　loaded　FGM　plate　with　two　simply　supported　opposite　and　two　free　edges　subjected　to　the　in-plane　and　transversal　excitations　is　presented.　The　material　properties　of　the　FGM　plates　are　assumed　to　be　temperature　dependent　and　change　continuously　throughout　the　thickness　of　the　plate,　according　to　the　volume　fraction　of　the　constituent　materials　based　on　the　power　law　function.　The　temperature　is　assumed　to　be　constant　in　the　plane　and　varied　only　in　the　thickness　direction　of　the　plate.　The　plate　is　modeled　by　using　the　Von　Karman　hypothesis　and　the　equations　of　motion　are　obtained　by　using　an　energy　approach.　It　is　our　aim　to　choose　a　suitable　mode　function　to　satisfy　the　first　two　modes　of　transverse　nonlinear　oscillations　and　the　boundary　conditions　for　the　FGM　rectangular　plates　with　two　simply　supported　opposite　and　two　free　edges.　The　equations　of　motion　can　be　reduced　into　a　two-degree-of-freedom　nonlinear　system　of　transverse　motion　under　combined　thermal　and　external　excitations　by　using　the　Galerkin＇s　method.　By　the　numerical　method,　the　nonlinear　dynamical　equations　are　analyzed　to　find　the　nonlinear　responses　of　the　FGM　plate　with　two　simply　supported　opposite　and　two　free　edges.　Under　certain　conditions　the　periodic　motions　and　the　chaotic　motions　of　the　FGM　plate　are　found.　The　bifurcation　diagram　demonstrates　that　for　a　certain　geometric　and　material　properties　the　chaotic　responses　of　the　plate　exist　as　the　transverse　excitation　changes.　Moreover,　numerical　simulations　also　illustrate　that　the　deflections　of　the　nonlinear　dynamic　of　the　FGM　rectangular　plate　are　larger　than　that　of　the　periodic　motions.