In a coupled structural-acoustic system which has a box structure and interior air the position of a defect included in the structure is identified by using the frequency response of sound pressure level in the interior sound field. For the analysis of coupled structural-acoustic system Finite Element Method (FEM) is utilized. The box including a defect is excited by dynamical load and the frequency response of the interior sound are learned by Self-organizing Maps (SOM) as an input vector and the map is drawn in the 2-dimensional plane. The frequency response for the model whose defect position is not known is given to the trained map, and the identification is carried out. As a result the good accuracy of the identification is obtained. Furthermore, it is confirmed that the identification by SOM is better than by the other neural network such as LVQ (Learning Vector Quantization) or BNN (Back Propagation Neural Network).