Reduced ascorbic acid,one of water-soluble vitamins,widely contained in fruits and vegetables,was studied for its loss under low power ultrasonic bath. The influence of ultrasonic power( 0. 05,0. 15,0. 25,0. 35,0. 45W / cm2),frequency( 28,40,50,135 kHz),cleaning time( 5,10,15,20,25 min) on the loss of reduced ascorbic acid were studied. The results showed that the loss rate of reduced ascorbic acid increased with the increase of ultrasonic cleaning power and the length of cleaning time. In contrast,the loss rate decreased with the increase of ultrasonic frequency. In addition,under the ultrasonic condition of 28 kHz and 0. 45 W / cm2,the loss rate of reduced ascorbic acid was the highest which was 61. 36% loss after 25 min ultrasonic treatment. At 135 kHz and 0. 05 W / cm2,the loss rate of reduced ascorbic acid was the lowest of 9. 94% loss after 5 min ultrasonic treatment.