Many interrelated factors must be considered in the design of an electronic system. Finding the optimum design condition having been subjected to various design constraints is often not a trivial matter. Utilizing an approach to optimize the design of electronic systems would have many advantages. A design optimization approach allows designers to study and optimize the various design alternatives. To illustrate this approach, in this study the optimum design of electronic enclosures from the viewpoint of electromagnetic shielding effectiveness is considered. An optimization problem has been formulated and the influence of several design variables in the definition of the objective function and constraints set is examined. To solve the problem, a non-linear optimization solution technique is utilized that allows users to optimize an objective function bound by equality and inequality constraints. A case study is presented to illustrate the utility of this technique in selection of the best composite materials for maximum absorption against radiated energy, a case with application in radar.