Abstract This paper investigates nonlinear bending and postbuckling behavior of functionally graded sandwich plates resting on elastic foundations and subjected to uniform external pressure, thermal loading and uniaxial compression in thermal environment. The material properties of both face sheets and core layer are assumed to be temperature-dependent, and effective material properties of FGM layers are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents. Formulations are based on first order shear deformation theory taking von Karman nonlinearity, initial geometrical imperfection, Pasternak type elastic foundations and tangential edge constraints into consideration. Approximate solutions are assumed and Galerkin procedure is applied to derive nonlinear relations of load and deflection. In thermal postbuckling analysis, an iteration algorithm is adopted to obtain buckling temperatures and postbuckling curves. The effects of material, geometry and foundation stiffness parameters, face sheet thickness to total thickness ratio, imperfection and degree of tangential restraint of edges on the nonlinear bending and postbuckling behavior of FGM sandwich plates are analyzed and discussed in detail.