The aim of this work is to investigate the geometrically non-linear free and forced vibration analysis of fully clamped rectangular and skew plates, for the isotropic, composite laminated and functionally graded materials plates. Theoretical model used was based on Hamilton's principle and spectral analysis. Maximal transverse vibration versus nonlinear frequency parameter for the fundamental mode shape was obtained, and the associated non linear bending and membrane stresses were calculated using an averaging technique taking in to account the influence of the axial displacement for different skew angles and aspect ratios. The geometrically non-linear free vibration of fully clamped symmetrically laminated composite skew plates was studied. A convergence study has been performed and analysis was given for the linear and non-linear fundamental mode shape considering different parameters such as the skew angle, the number of layers, the fiber orientation, the vibration amplitudes and plate aspect ratio. The geometrically non-linear free vibration of fully clamped functionally graded skew plates (FGSP) was examined.