The article deals with the quality estimation for the mechanical balancing of flexible rotors in a high-speed balancing facility by vibration measurements on rotating shafts. It is proposed a calculation-experimental method that would estimate the quality for the mechanical balancing of flexible rotors like the criteria by vibration measurements on non-rotating parts. The requirement of uniformity of dynamic reactions of the non-rotating parts of balanced rotors is used as a single criterion for the balancing quality. The dynamic responses ofbalanced rotors supports are measured directly ifthe vibration is measured on non-rotating parts. It is needed a simple and reliable calculation method of the dynamic responses of balanced rotors supports if the vibration is measured on rotating shafts. The proposed estimation method of the balancing of flexible rotors according to the supports dynamic loads level allows to substantiate quantitative values of balancing quality criteria. This allows making uniform criteria for the balancing of flexible rotors, regardless of vibration control methods and balancing facility. This is an important requirement at the current level of world production globalization. In addition, the proposed criteria for the balancing of flexible rotors allow to compare the balancing quality of different rotor types, which, moreover, is carried out on supports of different stiffness.