Abstract: A method based on the genetic algorithms is developed for the estimations of structural damage using the measured dynamic data. Some improved strategies, for instance, multi- parents crossover and fine-tuning of variables, are introduced to detect the damage of a fixed-end beam, and satisfactory results are obtained in the paper. In the calculation, two groups of data are used as inputs of the genetic algorithms, that is, the first two order natural frequencies and the corresponding vibration modes and the first three natural frequencies and the first vibration mode. It is concluded that optimum is achieved successfully by using the genetic algorithms with less data.