In this paper, a new method is developed to quantify the defect due to porosity in a composite structure using the principle of wave propagation in structures. A model developed, based on a modified rule of mixture is used to include the influence of porosity on the stiffness and density of the composites. The values thus obtained from the modified rule of mixture model are used in a conventional spectral finite element model to develop a new model for solving wave propagation problems for porous laminated composites. The influence of the porosity content on the spectrum relations, dispersion relations and the velocity responses is studied first, in the forward problem. These numerically obtained responses are further used for the estimation of porosity in a measured response, by solving a nonlinear optimization problem.© (2011) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.