Continuous exposure to high-energy ultrasonic waves depolymerises macromolecules in solutions and produces a permanent reduction in viscosity. Different factors affect the efficiency of this ultrasonic depolymerisation. In this work ultrasonic degradation of one commercially important hydrogel based on acrylic acid and acrylamide was carried out in aqueous solution at room temperature (25^oC). Also, the effect of sonication parameters (power and cycle) on the rate of degradation was investigated. A method of viscometry was used to study the degradation behaviour of the hydrogel and a first order kinetic equation was developed to calculate the degradation rate constants. The experimental results indicated that the rate of ultrasonic degradation increased with increasing ultrasonic power and pulse. FT-IR spectrometry measurements confirmed that the degradation proceeds by mechanical forces. Finally a mechanism was proposed according to the experimental data.