Com. caffeic acid was dissolved in EtOH and MeOH and treated with ultrasonic iradn. (21 W/cm(2) and 38 W/cm(2)). A field of acoustic waves with a frequency of 20 kHz for 0-30 min was used. The content of caffeic acid was detd. by using. chromatog. and Folin-Ciocalteu methods. According to the chromatog. method, no statistically significant effect of ultrasound on the stability of caffeic acid was found. A decrease in the concn. of caffeic acid in soln. after sonication was obsd. in the case of Folin-Ciocalteu method. An antioxidant activity of caffeic acid was elso evaluated by using 2,2-diphenyl-1-picrylhydrazyl radical.