Abstract: The longitudinal-torsional composite mode ultrasonic transducer is studied. The transducer consists of the front and back exponential metal horns, and the axially and tangentially polarized piezoelectric ceramic piles. The resonance frequency equations for the longitudinal and torsional vibrations in the transducer are derived. By changing the cross sectional radius decay coefficient of the exponential metal horns, the longitudinal and torsional vibrations in the transducer could resonate at the same resonance frequency. Experimental results show that the measured resonance frequency is in good agreement with the theoretical results, and the resonance frequency for the longitudinal vibration is basically the same as that for the torsional vibration in the transducer. This kind of transducer could be used in ultrasonic processing and other high power ultrasonic technologies.