While designing the metallic enclosure for the electromagnetic shielding of electronic circuits, apertures on the enclosure walls become unavoidable for the purpose of signal cabling and ventilation. The Conventional Enclosure design involves a repeated procedure where the hole position and locations are varied until the Shielding Effectiveness (SE) requirements met. In this paper Double Layer Frequency Selective Surface (DLFSS) is used to construct the walls of the SMPS Enclosure which involves simple procedure. The FSS constructed from Greek Cross type apertures, etched on the conducting walls without any dielectric substrate (to enable ventilation) act as a spatial band-pass filter. Even though the design objective of the EM Shielding Enclosure is all-stop filter characteristics, the ventilation requirement impose the enclosure to allow certain band of EMI to pass. So the DLFSS is designed to pass a band of EMI at 15GHz which is acceptable to satisfy the EMC and ventilation requirements. DLFSS and Conventional SMPS enclosures are modelled and shielding effectiveness is calculated and compared. © 2011 IEEE.