Abstract: A novel Information-gap-based (Info-gap) damage detection method for uncertainty quantification is proposed in this study. The modal shapes of structures are selected as damage indices, and the uncertainty level of these indices caused by measurement errors and modal identification are described by Info-gap model. The decision function is defined as the distance of modal shape between health and unknown condition of structures, and then the solution of this function is translated into an optimization problem. The results from a numerical simulation and lab-scale structure show that the location and severity of damage can be successfully identified.