The　nonlinear　oscillations　and　resonant　responses　of　the　symmetric　cross-ply　composite　laminated　plates　are　investigated　theoretically　and　experimentally.　The　governing　equations　of　motion　for　the　composite　laminated　plate　are　derived　by　using　the　von　Karman　type　equation,　Reddy＇s　third-order　shear　deformation　plate　theory,　and　Galerkin　method　with　the　geometric　nonlinearity.　The　four-dimensional　averaged　equation　is　obtained　by　using　the　method　of　multiple　scales.　The　frequency-response　functions　are　analyzed　under　the　consideration　of　strongly　coupled　of　two　modes.　The　influences　of　the　resonance　case　on　the　softening　and　hardening　type　of　nonlinearity　are　analyzed　with　different　parameters　for　the　composite　laminated　plates.　The　numerical　results　indicate　that　there　exist　the　hardening　and　softening　types　of　the　composite　laminated　plate　in　the　specific　resonant　case.　The　variation　of　the　response　amplitudes　is　studied　for　the　composite　laminated　plate　under　combined　the　transverse　and　in-plane　excitations.　A　sweep　frequency　experiment　is　performed　to　obtain　the　hardening　and　softening　nonlinearities　of　a　composite　laminated　plate.　The　experimental　results　coincide　with　the　numerical　results　qualitatively.　The　influences　of　the　excitation　amplitudes　on　the　softening　and　hardening　types　of　nonlinearity　are　also　analyzed　for　the　composite　laminated　plate.　The　amplitude　spectrums　of　the　test　plate　also　demonstrate　that　the　change　of　the　nonlinear　dynamic　responses　may　be　caused　by　the　subharmonic　resonance.