Maximum degradation of potato starch was detected after 30 min sonication at l‐2°C. Degradation, evidenced by decrease in viscosity, may occur to starch granules rather than the individual polymers. This hypothesis was supported by the fact that no difference in rate of enzymatic hydrolysis was detected between sonicated and nonsonicated potato starch when either was used as substrate for β‐amylase. Neither the specific activity of pure preparation of β‐amylase, nor its electrophoretic behavior was altered due to cavita‐tion action of sonication. Ultrasonic waves also did not alter activities of β‐amylase intrinsic of sweet potato. Copyright © 1979, Wiley Blackwell. All rights reserved