To predict electromagnetic field distribution inside a loaded enclosure with the aperture, we present a hybrid formulation which combines method of moments and finite element method. To predict efficiency of the method, the shielding effectiveness of an empty enclosure is compared with the literature. Then the method is applied to dielectric slab loaded enclosure with the single aperture, and the shielding effectiveness, ratio of stored electrical energy, and dissipated power variations are obtained. (C) 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE 19: 204-210. 2009.