The dynamic behavior of machines which rotate at extreme high speeds is crucial for stable and long operation. In design process some dynamics calculation must be taken into account to avoid potential operation near resonance areas. This paper considers dynamic analysis of the high speed reducer, designed together with the turbo-shaft engine. Resonances can occur when frequency of rotation and teeth mesh frequency are close to gear pair in mesh natural frequency, to the shafts natural frequencies and to the other parts natural frequencies. Problems can be avoided by translating resonant areas to higher or lower level of frequency by changing some design parameters, mass, stiffness and by variation of the stiffness of bearing supports. The paper presents the approaches to natural frequencies identification for the example of high speed reducer design. Some examples of design solutions, especially for elastic bearing supports and their experimental testing are also presented.