To improve the efficacy of sonodynamic therapy of cancer using photosensitizers, we developed a novel porphyrin derivative designated DCPH-P-Na(I) and investigated its photochemical characteristics and sonotoxicity on tumor cells. DCPH-P-Na(I) exhibited a minimum fluorescent emission by excitation with light, compared with a strong emission from ATX-70, which is known to reveal both photo- and sonotoxicity. According to this observation, when human tumor cells were exposed to light in the presence of DCPH-P-Na(I) in vitro, the least phototoxicity was observed, in contrast to the strong phototoxicity of ATX-70. However, DCPH-P-Na(I) exhibited a potent sonotoxicity on tumor cells by irradiation with ultrasound in vitro. This sonotoxicity was reduced by the addition of L-histidine, but not D-mannitol, thus suggesting that singlet oxygen may be responsible for the sonotoxicity of DCPH-P-Na(I). DCPH-P-Na(I) demonstrated significant sonotoxicity against a variety of cancer cell lines derived from different tissues. In addition, in a mouse xenograft model, a potent growth inhibition of the tumor was observed using sonication after the administration of DCPH-P-Na(I) to the mouse. These results suggest that sonodynamic therapy with DCPH-P-Na(I) may therefore be a useful clinical treatment for cancers located deep in the human body without inducing skin sensitivity, which tends to be a major side-effect of photosensitizers.