In mixed finite element formulation, the fundamental difference among the various approaches depend on the variational principles such as the Hellinger-Reissner, the Hu-Washizu and the Gateaux differential which is introduced by Omurtag et al. [5-9] to the literature in the recent years. In this paper, a functional for interaction of orthotropic plate-foundation is obtained by using the Gateaux differential and rectangular mixed finite elements PLTEOR4 and PLTEOR9 are formulated explicitly. Foundation is modeled as a Pasternak type which can be either isotropic or orthotropic and as a special case it converges to Winkler foundation if the shear layer is neglected. Using the mathematical advantages of the proposed variational method a functional with proper geometric and dynamic boundary conditions, introduced from the field equations of the plate and the foundation, is explicitly given. Copyright (C) 1996 Elsevier Science Ltd.