Sonochemical oxidation has a promising future in the area of waste water treatment as one of the advanced oxidation methods. In this study, direct ultrasonic degradation of acetic acid was investigated in low powers (0.1-0.4 W) and in a frequency range of 30-100 kHz. An ultrasonic transducer was used for sonication. The results showed that there was an optimum frequency at 60 kHz for direct sonication of acetic acid and degradation rate increased up to a power of 0.2 W and then it decreased. Sonochemistry is associated with the bubble of cavitation which depends on the sound pressure field and nature of molecule. Therefore, the frequency and intensity have to be optimized for the minimization of energy requirement during waste water treatment with ultrasound.