Chemical agents such as hematoporphyrin have been found to have a sonochemical activity to induce anti-tumor effects. The same kind of sonochemical reactions producing active oxygen species has been demonstrated to be localized with a highly focused ultrasound in a specially developed tissue-mimicking phantom. These results suggest that the focused ultrasound irradiation to a tumor combined with administration of such a sonochemically active agent can be a potential low-invasive modality for cancer therapy.