There is a growing interest in developing non-destructive damage detection methods for damage assessment of composite structures, especially in the aerospace and marine industries. Although damage detection of composite laminates has been widely investigated, little work has been carried out on sandwich composite configurations. A technique using the Lipschitz exponent, which is estimated by wavelet transforms, as a damage sensitive signal feature is outlined here to identify damage in sandwich composites. It is based on the fact that damage causes singularities to appear in the structure's dynamic response which can be identified, and its severity estimated, using the Lipschitz exponent. In order to demonstrate this technique, damage in cantilevered fibre reinforced plastic (FRP) sandwich beams is investigated both numerically and experimentally.