Ultrasonic motors (USM) which has many useful features such as small, light and high torque at low speed are expected to find many applications in several fields. However it is difficult to control precisely since the USM contains nonlinear properties caused by driving frictions, changes of temperature, fluctuation of load-mass and so on. To date, a large number of studies have been made on the compensation of the USM nonlinear properties using neural network, fuzzy control and other position control theories as well. However, studies aiming at holding the optimal tracking performance of the USM designed for nominal plant have not been reported yet. Accordingly, in this paper, we propose a position control method of the USM using a two-degree-of-freedom optimal servo system with an adaptive technique. The effectiveness of the proposed method is well demonstrated based on the results of our experimental study.