The dynamic behavior of structures, in particular, that of a rotor, containing cracks is a subject of considerable current interest. In the present study, the influence of a transverse surface crack, both open and breathing conditions, on the mechanical impedance of the rotor-bearing system, has been investigated by FEM analysis for flexural vibrations. The results show that the mechanical impedance changes substantially due to the presence of crack and follow definite trends with the crack parameters (depth and location) and force location. The normalized mechanical impedance of rotor system is more sensitive to the breathing crack when compared to the open crack. The sudden changes in mechanical impedance have been observed at the multiples of the running frequency for the breathing crack. The measurement of mechanical impedance has been suggested for crack detection and condition monitoring of rotor-bearing systems. © 2001 Acoustical Society of America.