Recently, road cave-in and depression in urban area due to subsurface cavity are emerging as a social issue in Korea. These phenomena enable to cause not only damage to human lives and properties, but also an anxiety of the citizens. Furthermore, it is a problem that needs more fundamental solution to countermeasure. The objective of this study is to evaluate the stiffness characteristics of asphalt pavement with existence of subsurface cavity using Falling Weight Deflectometer (FWD) deflection and backcalculation analysis using GAPAVE program developed the KICT. The characteristics of FWD deflections are analysed for cavity and intact asphalt pavements. The stiffness reduction in the asphalt pavement due to subsurface cavity was evaluated as a result of this FWD test. The Seoul Metropolitan Government has conducted a Ground Penetrating Radar (GPR) test, coring, and image photographing in four different locations to determine the presence of the cavity and figure out the cavity depth and size underneath asphalt pavements. The cavity depths measured in this section range between 17cm to 51cm, and its lengths are at least 70cm to up to 310cm. It is found from this analysis that the deflections measured from cavity section are generally higher than intact section in same locations. As results of backcalculation analysis, it appears that the backcalculated moduli are generally decreasing with increase of cavity depth. After comparing with AC moduli obtained from intact and cavity section, it is observed that about 80% of moduli was reduced with existence of subsurface.