Abstract: Load characteristics of ultrasonic rotary motors using longitudinal-torsional vibration convertor with diagonal slits under various friction pairs were studied. Applying various friction materials to the surfaces of stator and rotor,various friction pairs of hard/soft,soft/hard,hard/hard were got. The motor has low velocity,small torque and low efficiency when the soft/hard friction pairs are adopted. However,the load characteristics are significantly improved when the hard/soft friction pairs are adopted. Experiments show when the tooth are cut and formed on the surface of the stator,the wear and tear of the friction surface is reduced,the motor operates smoothly,and load characteristics are improved. 15 mm-diameter prototypes were developed,maximum torque over 0.32 N·m,velocity of 1 325 r/min and efficiency of 32.3% are obtained.