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This paper presents a new approach for compliance control using a traveling-wave ultrasonic motor. Its objective is to demonstrate the effectiveness of using duty ratios and frequencies as control variables for both preload and stiffness control. At the home position, the motor is engaged in a standing-wave mode operation and provides self-locking torque. When the motor is deflected, it is engaged in a traveling-wave mode operation to provide a reacting torque. The torque is varied according to the deflection to provide the desired stiffness. Experiments have confirmed the effectiveness of this method. This approach can also be readily deployed into many force-feedback and haptic applications such as robotic locomotion.