The removal performance of chlorinated organic compound from the porous material under the ultrasonic irradiation was experimentally investigated. As the model PCB and the solvent, o-dichlorobenzene and hexane were used. Wood chips impregnated with o-dichlorobenzene were used as the sample. By the ultrasonic irradiation, the removal ratio rapidly increased and became almost unity after 120 min for the sample with 10 rum in length. The removal rate for the ultrasonic irradiation was much higher than that for shaking. The difference in removal ratio between the ultrasonic irradiation and the shaking became larger as the sample was bigger. The removal ratio increased with increasing sound pressure and became constant beyond a certain sound pressure. Under a fixed sound pressure, the removal ratio at 28 kHz is nearly equal to that at 45 kHz.