From a mechanical point of view, when a plate is subjected to compressive in-plane loads and tends to go out of the loaded plane, the buckling phenomenon has occurred. The buckling, which occurs as a result of compressive in-plane loads, structural defects, eccentric loads, etc, leads to structural instability and damage to structures. In this thesis nonlinear unilateral buckling analysis of laminated composite plates with sensor and actuator piezoelectric layers has been studied. The plate is placed on a unilateral elastic foundation is not able to apply tension load. This is due to unilateral constraint and loads to a nonlinear buckling problem. The unilateral buckling of plates is in fact a contact problem. The stability analysis of plates resting on foundations, e.g concrete beam/column-reinforced-plates, etc, are some of its practical usages. Different kinds of in-plane loads are induced in the plate because of mechanical, electrical and thermal loads or a combination. For the analysis of this behavior,both Rayleigh-Ritz and finite element methods are used based on classical plate theory . In finite element method, a rectangular 4 node conforming element scheme with 16-DOF element for out-of-plane behavior and 8-DOF elementsfor in-plane behavior are used.In Rayleigh-Ritz method, Khayyam-Pascal polynomial for out-of-plane behavior, and hierarchical interpolation functions for in-plane behavior are implemented. Finally the effects of Young’s modulus ratio, fiber orientation, plate aspect ratio, different boundary conditions, the number and arrangements of layers, the presence of sensor and actuator piezoelectric layers, electrical conditions and the magnitude of control gain are studied severity of the loads, temperature and critical bilateral and unilateral buckling voltages, respectively, excited by mechanical, thermal and electrical loads or a combination. All previous researches on the unilateral buckling of plates are limited to single-layer isotropic plates. The simulated results are compared with previous works which have studied the unilateral buckling of single-layer isotropic plates resting on elastic foundation, free of interaction with any foundation buckling of both symmetric and unsymmetric laminated composite plates, excited by mechanical, thermal and electrical loads or a combination. The numerical results are validated satisfactorily for both numerical methods and their accuracy and reliability have been confirmed. Keywords: Unilateral buckling, Rayleigh-Ritz methods, Finite element methods, Kirchhoff theory, Sensor and actuator piezoelectric, Thermo-electro-mechanical loading