Dynamic behavior of a piezothermoelastic symmetrical cross-ply rectangular laminate subjected to mechanical, thermal and electrical loads and simply-supported is investigated considering the effect of damping. The strain of the laminate is expressed by the dynamic deflection based on the classical layered theory and the von Karman theory. Then the stress of laminate is expressed by the strain as the constitutive equation. Using the von Karman strain and the piezothermoelastic constitutive equations, the equations of motion in terms of displacements are obtained. Then, the equations of motion are solved by the Galerkin method. The differential equation obtained by the method is analyzed by using Runge-Kutta method. Thereafter, we present the dynamic behavior of a piezothermoelastic laminate subjected to constant mechanical, thermal and electrical loads.