Engineering structures which are based on laminated composites have a high probability of unexpected damage developing during service. The damaged formations must be monitored from the beginning before they head towards structural failure which could result in substantial damage. This leads to the necessity of a structural health monitoring (SHM) system to be installed during the construction of laminated composite structures. However, an understanding of damage area detection and damage characteristics is essential before a SHM system can be integrated into the structures. This article presents the effects of wave propagation through an existing area of damage on composite plates. Theoretically, a propagating wave that starts from any source will vary when crossing an area with damage. This study shows that high frequency wave propagation (kHz range) reacts differently when passing through the damaged area, compared with low frequency wave propagation. The results of the study will lead to an effective damage detection method, utilizing the available vibration source, especially for the condition monitoring of thin laminated composite structures.