In the present paper, a new combined technique consist of experimental results and numerical solution for determination of elastic constants of thin and thick orthotropic plates with various stacking sequences; and also isotropic plates under different boundary conditions is proposed. This new proposed technique makes use of vibrational test data, corresponding numerical solution and optimization methods. The vibration test data consists of a set of eigen frequencies that are obtained from transverse vibration test of the plate. The numerical solution is based on a finite element method using a commercial program. Material constants of the plate are determined by using of the inverse method and a particle swarm optimization algorithm in MATLAB software. The error function is based on the sum of square difference between experimental data and numerical data of eigen frequencies solution. The validation, performance and ability of the proposed technique in this paper are discussed using experimental and numerical data available in the literature. The higher accuracy of results that obtained by the present method in comparison with other methods proved the validity and capability f the new proposed method.