An important aspect of the concept of smart structures is the automated structural health monitoring of the structure. This paper presents a new approach to detect the damage in composite structures and applications of artificial neural networks in the damage identification. The approach is based on the neural network to deduce the damage size and location from the change of structural dynamic properties. A neural network is trained with the natural frequencies of the first-five modes obtained from finite element analyses of composite beams with various delaminations. The effectiveness of neural networks trained by various properties was discussed for determining the location and size of any delaminations.