Abstract: In this paper, the existence of the solution for the Most Economical Information Structure (MEIS) problem is discussed. A criterion for determining the fixed modes as well as their multiplicities, applicable to arbitrarily restricted feedback structure, is then given. This criterion provides the possibility to evaluate the contributions of all single feedback elements and their combinations to the removing of the open-loop poles and thus furnishes the necessary information for synthesizing the MEIS. On this basis, the authors present a recursive algorithm for synthesizing MEIS and propose the design procedure of decentralized control systems with the MEIS. Finally, a numerical example is given for illustration.