In the proposed project¡Athe three - dimensional vibration of circular and annular plates is analyzed by a mixed finite element¡C Stresses¡Aas well as displacements¡A are primary variables in the mixed finite element formulation¡Atherefore¡Aall the stress and displacement boundary conditions can be imposed exactly¡CMeanwhile¡Athe proposed finite element is a modification of axisymmetric finite element which is based on three ¡V dimensional elasticity¡Aso general results of both axisymmetric and unaxisymmetric vibration of circular and annular plates can be obtained¡C Results of the present project will be compared to those by conventional displacement ¡V type finite element¡ARitz method and series method to show the difference among these theories¡CEspecially¡Athe effect of satisfying the stress boundary conditions on the unaxisymmetric vibration analyses can be demonstrated¡Awhich is not available in the literature up to date¡C