Delamination detection in the composite structure based on the vibration responses when excited at the lower modes has been suggested here. It has been observed that the nonlinear interaction between the delaminated layers produce higher harmonics of the exciting frequency. These higher harmonics have observed to be useful for the detection and location of the delamination without comparing the vibration data from the healthy state of the composite structure. The paper presents the observation based on the finite element analysis of a composite plate with and without delamination and then on the experiments on the composite plates with and without delamination.