Abstract In this paper, we investigate the application of modal identification techniques used in civil structures, in which the excitation forces are not known, and extrapolate them to mechanical elements in operating conditions. A methodology is proposed to identify the modal parameters of a power transmission shaft under rotation. The methodology is based on the comparison of theoretical and experimental results. First, a simulation of the element under study is carried out, using a numerical model based on the Finite Element Method, to evaluate its theoretical dynamic characteristics. Then, an Experimental Modal Analysis (EMA) is performed and the theoretical model is verified by comparing theoretical and experimental results. Moreover, an algorithm based on the non-parametric technique “Peak Pickin” of an Operational Modal Analysis (OMA) is developed and, from the records of accelerations obtained in the bearings, we identify the modal parameters of the shaft. These results are compared with the theoretical values, calculated previously and, thus, verify the effectiveness of the implemented technique.