Abstract: This paper proposes a rigorous full-wave solution which combines the mode-matching technique and the mixed potential integral equation based on the method of moments to analyze the shielding effectiveness of the metallic rectangular cascaded enclosure with apertures. Some influence factors, such as the dimension of enclosures, the orientation of apertures, the polarization direction of the incident wave and the high-order modes propagating in enclosures, are considered. The accuracy and the efficiency of the proposed approach are validated by comparing with the classical algorithm. Finally, some conclusions are derived: the shielding performance of cascaded enclosures is better than that of single-stage enclosures, the shielding effectiveness can be improved with increasing the distance between stages in the range, and the shielding performance of the double-stage enclosure with parallel-pattern apertures in horizontal polarization case is better than that in vertical polarization case, but similar advantage is not obvious for enclosures with cross-pattern apertures.