Abstract: This paper discribes the procedure of Ibrahim time domain identification method and least-square time domain method for identifying the modal parameters of vibrating structures. The results of identification of the natural frequencies and damping factors by utilizing multiple free-response measurement data obtained from the lateral vibration test of a diesel propulsion plant and the torsional vibration test of a model which is made up of three disks and shafts are presented. The frequencies identified in both testings structures are similar to that obtained by using spectrum analysis of vibration response. In this paper, the characteristics of these algoritlms and some ways for taking data samples are also discussed.