In this paper, the effects of transverse cracks on rotating shaft were studied. According to earlier works, crack shaft failure decrease the critical speed of the shaft and also exhibit a nonlinear vibration behaviour leading to increases the amplitude of 1X and 2X harmonics (first and second order of rotational speed in torsional vibration). This suggests that the application of order analysis to be very effective. Moreover, vibrations arising from resonance frequencies of the system can be differentiated from other ones, by using this method. For this purpose in this article, first, un cracked and cracked shaft were mathematically modelled and numerical analysis was carried out to obtain the vibration response for both healthy and faulty shaft. Then order analysis method was applied on the vibration signals obtained from the model. Finally, an experiment was also carried out on a laboratory scale test rig to verify effectiveness of the order analysis in practice. The results show that the vibration orders arising from torsional vibration can be clearly sensed by the transducers installed on the supports which primarily measure the bending vibrations. تفاصيل المقالة