The ultrasonic degradation of phenol in water was carried out in the presence of the composite particles of anatase-type TiO2 and activated carbon. The effects of the added amount of the particles and the AC/TiO2 ratio in the composite particles were also investigated. The phenol concentration monotonically decreased for all conditions. In cases that TiO2 particles were suspended, the phenol concentrations were almost same as those without TiO2. The lower phenol concentration in the presence of the activated carbon or composite particles was responsible for the adsorption of the phenol on the activated carbon. In case that both TiO2 and activated carbon were simply suspended, the phenol concentrations were also the same as those without TiO2. On the other hand, the phenol concentrations for the composite particles were much lower than those for the activated carbon. The results suggested that the ultrasonic irradiation to the composite particles was highly effective for the degradation of phenol. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).