Honeycomb　sandwich　structures　have　been　widely　used　in　many　engineering　fields　because　of　their　excellent　mechanical　properties.　The　formulas　for　the　cantilever　honeycomb　sandwich　plate　are　derived,　and　the　nonlinear　vibrations　of　the　plate　are　given　in　this　paper.　In　order　to　obtain　the　equivalent　elastic　parameters　of　the　hexagonal　core　layer　in　the　honeycomb　sandwich　plate,　the　equivalent　elastic　parameters　that　more　closer　to　the　finite　element　solutions　for　the　cores　are　selected.　Based　on　the　Reddy＇s　third-order　shear　deformation　theory,　the　nonlinear　partial　differential　equations　of　motion　are　derived　for　the　composite　laminated　cantilever　plate　subjected　to　in-plane　and　transverse　excitations　by　using　the　Hamilton＇s　principle.　The　Galerkin　method　is　then　used　to　transform　the　nonlinear　partial　differential　equations　of　motion　to　a　two-degree-of-freedom　nonlinear　system　ordinary　differential　equation　of　motion.　The　numerical　method　is　also　utilized　to　examine　the　nonlinear　dynamic　responses　of　the　cantilever　honeycomb　sandwich　plate.　The　results　show　that　in-plane　and　transverse　excitations　have　an　important　influence　on　nonlinear　dynamic　characteristics,　and　periodic,　multi-periodic,　quasi-periodic　motions　and　chaotic　motions　all　occur　for　the　system　with　the　change　of　forcing　loads.