Abstract: A new method is proposed to identify structural damages only by changing the natural frequencies of the structure. By adding given masses to the physical structure, measuring the lower natural frequencies of the mass-modified structure, and then using these new data as well as the original test information, structural damages can be detected by using the eigenvalue perturbation technique. Regardless of whether the structure is unsymmetrical or symmetrical, the proposed method can successfully identify damages even if only the first few natural frequencies are measured. The approach offers the practical attraction of only requiring measurements of the changes in a few of the structural natural frequencies between the undamaged and damaged states. The paper also discussed the means of determining the number, placement and size of the added masses. The feasibility of the methodology is demonstrated analytically on a symmetrical beam structure. Results show that the proposed method may be a promising tool to be used in structural damage identification.