During the service life, offshore structures continually accumulate damage as a result of applying the various environmental forces. Clearly the development of strong techniques for early damage detection is very important to avoid the possible occurrence of a disastrous structural failure. Most of vibration-based damage detection methods require the modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such a good sensitive indication of structural damage. The wavelet packet transform (WPT) is a mathematical tool that has a special advantage over the traditional Fourier transform in analyzing non-stationary signals. In this study, a damage detection index called wavelet packet energy rate index (WPERI), is presented for the damage detection of offshore jacket structures. The measured dynamic signals are decomposed into the wavelet packet components and the wavelet energy rate index is computed to indicate the structural damage. It is shown that this method can be used for damage detection of this kind of structures.