The acceleration effects on Fenton's reaction upon exposure to ultrasonic irradiation were evaluated in order to utilize this reaction to effectively remove volatile organic compounds from soil and groundwater. The decomposition reaction kinetics of trichloroethylene (TCE) by Fenton's reaction were investigated before and after the application of ultrasonic irradiation, namely, the sonochemical reaction. Fenton's reaction was evaluated using 0.5 mol L-1 or 1.2 mol L-1 of hydrogen peroxide and various concentrations (1-5 mmol L-1) of ferrous ions. The ultrasonic frequency was fixed at 176.9 kHz, and the reaction rates were evaluated as first order reaction kinetics in terms of TCE. The rate of Fenton's reaction in conjunction with ultrasonic irradiation was found to be higher than the combined individual rates of Fenton's reaction and the sonochemical reaction, even though the reaction rates were dependent on the concentrations of hydrogen peroxide and ferrous ions. These results suggest some synergistic effects between Fenton's reaction and the sonochemical reaction on the decomposition of TCE. The following two mechanisms were considered to be the reason behind this synergistic effect: 1) the added effects of the nitrous or nitric acid generated by the sonochemical reaction or 2) the acceleration of Fenton's reaction by hotspots generated through ultrasonic irradiation.