Critical facilities are very attractive targets for the terrorist attacks as they have a significant impact to the psychology, health and welfare of the population, and are essential to the operations of the economy and government. The initial and crucial step for a realistic risk management against this threat is the vulnerability assessment that necessitates a structured quantified methodology. In this study, a fuzzy analytic network process (FANP) based vulnerability assessment approach is presented to determine the vulnerability of such a critical facility under multiple qualitative and quantitative criteria. This model also considers the possible interdependencies among the functions of the facility. An airport example illustrates the proposed approach.