Abstract: A damage detection procedure applied to mono-coupled periodic systems using a sensitivity-based method is presented in this paper. The first order approximation of the natural frequencies with respect to one single damage in different elements is obtained and then used to form the sensitivity matrix. Consequently, the stiffness changes due to damage can be identified by solving a set of underdetermined equations based on the sensitivity matrix. For complex structures, there are many possible damage locations, a means of improving the computational efficiency of damage detection while maintaining the accuracy for large periodic structures with limited available measured natural frequencies is introduced. The theoretical analysis and numerical results show that the sensitivity of natural frequencies to damage in different locations depends only on the mode number and the location of damage, and the proposed method can locate correctly single or multiple damages in a large periodic structure.