Critical facility vulnerability assessment is a highly complex strategic activity in combating the terrorism and necessitates a structured quantified methodology to support the decision-making process in defense planning. In the system perspective, the critical facility, such as airport, dam, governmental facility, harbor, nuclear power plant, oil plant etc., can be defined as a system that relies on a group of different interdependent logical and physical entities as system functions and system components. The aim of this paper is to present a realistic approach to determine the vulnerability of such a system defended against the terrorist attack under multiple criteria which can be both qualitative and quantitative by considering these interdependencies. The proposed approach, called fuzzy integrated vulnerability assessment model (FIVAM), is based on fuzzy set theory, Simple Multi-Attribute Rating Technique (SMART) and Fuzzy Cognitive Maps (FCM) methodology in a group decision-making environment. The FIVAM approach is presented step-by-step and applied to a simple case study on airport vulnerability assessment. The results of the application are compared to those observed through a classical vulnerability assessment model to illustrate the effectiveness of the FIVAM. Furthermore, FIVAM provides a framework to identify the hidden vulnerabilities caused by the functional interdependencies within the system. The results also show that FIVAM quantifies the vulnerability of the system, system functions and system components, and determines the most critical functions and components by simulating the system behavior.