The nonlinear dynamics of simply supported honeycomb sandwich rectangular plates was investigated.Considering the effects of higherorder transverse shear deformation and transversal damping, we established the mathematical model of the honeycomb sandwich plates under the inplane and transversal excitations.The Galerkin method and numerical simulation were used to analyze the nonlinear responses of different amplitude excitations.The planar phase portrait,waveform and frequency spectrum were plotted.The results of numerical simulation indicate that there exists the following procedure of motion for the honeycomb sandwich rectangular plates under the inplane and transversal excitations:from periodic motion to chaotic motion and then to periodic motion.