Modeling of composite structures having smart piezoelectric sensors or actuators are very similar to conventional composite layered structures, however, there is one difference reflected in the constitutive laws in the form of the electromechanical coupling. It affects also the additional complexities in the FE formulation. The present formulation of optimal design introduces boundaries of piezoelectric patches as new class of design variables. In addition classical design variables in the form of ply orientation angles of orthotropic layers are also taken into account. The design objective is the minimization (maximization) of natural frequencies. The standard Rayleigh-Ritz method is used, however, the accuracy of optimal design are verified with the aid of the FE package ABAQUS. Examples are presented to illustrate the performance of the proposed model.