In this paper, the elastic and inelastic instability of isotropic and composite thick laminated plates with different end conditions are studied using the finite layer method (FLM). This method is an extension of the well-known finite element method, which efficiently transforms threedimensional problem into one-dimensional because of the trigonometric properties. By assuming appropriate interpolation for in-plane and out-of-plane displacements and using energy approach in conjunction with the assumption of deformation theory for inelastic buckling of each layer, the stiffness and geometry matrices are obtained. Afterward, these matrices are assembled and the eigen value problem is solved to obtain the elastic and inelastic critical buckling load. Numerical results are presented to demonstrate the accuracy and efficiency of the method.