Abstract Modal density of sandwich panels with composite face sheets and orthotropic core is presented based on an improved ordinary sandwich panel theory. The governing equations are derived by applying the Hamilton’s principle, where in-plane rigidity of the core is considered and the material and reference axes are not limited to be identical to each other. Modal density is obtained using wavenumber space integration, and the effects of boundary conditions on both modal density and mode counts are also studied. The accuracy of the proposed models is validated by comparing with the existing modal density expressions, piecewise shear deformation theory and finite element models. Parametric studies are performed in order to investigate the influence of the ply angle of face sheets and the core, in-plane rigidity of the core, transverse shear rigidity and boundary conditions on modal density. The proposed modal density formula has a wider application scope and will be beneficial to the predication of sound transmission and radiation of sandwich panels.