On　the　basis　of　laminated　plate　theory　and　piezoelectric　theory,　the　nonlinear　free　vibration　governing　equations　for　symmetric　cross-ply　moderately　thick　laminated　piezoelectric　plates　are　established.　The　Galerkin　procedure　furnishes　an　infinite　system　of　equations　for　time　functions　which　are　solved　by　the　method　of　harmonic　balance.　In　the　numerical　results,　the　influences　of　piezoelectric　effect　and　various　location　of　piezoelectric　layer　on　the　nonlinear　vibrating　frequency　of　the　laminated　piezoelectric　plates　are　discussed.　©　(2011)　Trans　Tech　Publications.