Buckling stresses and natural frequencies of cross-ply laminated composite plates are analyzed using new higher order shear deformation theory. The new displacement field proposed by J.L. Mantari et al depends on a parameter "m'', whose value is determined so as to give results closest to the three dimensions buckling solutions. A set of fundamental dynamic equations of a two-dimensional higher-order theory for rectangular laminated plates made of elastic and orthotropic materials is derived through Hamilton' s principle, these equations of motion are applied to solve the vibration and pre stressed free vibration problems of laminated composite plates after buckling solution. These equations are solved using Navier-type for simply supported boundary conditions. It was observed that this theory gives results close to three dimensions elasticity solutions and those obtained by existing shear deformation plate theories.