Abstract: To increase conversion efficiency from stator vibration to mechanical output of Cylindrical Ultrasonic Micro-Motors (C-USM), the slippage between the stator and the rotor should be reduced as much as possible. And the contact surface between a rotor and a stator should be vertical to the vibration locus of contact point to reduce the power loss. In this paper, a mathematical method will be demonstrated to determine the taper angle of contact surface of C-USM. Following the theoretical analysis, some prototypes φ5 mm × 15 mm, the different taper angle of contact surface were fabricated to give an experimental verification on this method. The theoretical and experimental results are in good agreement.