Composite sandwich panels have been employed in many structural applications. Therefore, it is very important to obtain the dynamical properties of the composite sandwich panels. Also, an inverse analysis method has already been proposed by one of the authors to identify the layer elastic parameters of laminated plates and shells using the FEM eigenvalue analysis and the nonlinear optimization algorithm. The purpose of this study is to improve the already proposed identification method to apply to a sandwich panel and to identify the equivalent core elastic parameters. By applying the experimental modal analysis technique to the sandwich panel, natural frequencies and mode shapes of the panel are obtained. From the obtained natural frequencies and mode shapes, the equivalent core elastic parameters are identified numerically. Furthermore, the usefulness of the improved identification method is clarified.