PDT is an established cancer treatment modality. This can be attributed to the attractive basic concept of PDT; Combination of two therapeutic agents, a photosensitizing drug and light, which are relatively harmless by themselves but when combined, cause more or less selective tumor destruction. Hematoporphyrin-derived photosensitizers are known to be stable and highly efficient. In this study, we conducted a series of experiments to develop light-induced anticancer drugs against oral cancer cells. We tested the cytotoxicity of photodin by MTT assay and observed cell death pattern (apoptosis or necrosis) by hoechst 33342 and propidium iodide staining methods after PDT. IC50 value of photodin was 0.65 ug/ml. At higher doses of photodin ( > 7.8 ug/ml), cancer cells died exclusively from necrosis after PDT. By contrast, at IC50 value, photodin induced cancer cell to undergo apoptotic cell death. The induction begins approximately 6 hours after PDT. We investigated intracellular localization of photodin by oral cancer cell via confocal laser scanning microscopy. Oral cancer cells dual-stained with photodin and organelle-specific fluorescence probes (Mitotracker, Lysotracker, ER-Tracker) revealed that an intracellular fluorescence distribution was restricted to cytoplasmic compartments with no detectable fluorescence in the nucleus. Confocal images of cells containing photodin were overlapped with the mitochondria-specific fluorescence probe images of the same cells. These results demonstrated that photodin may play the role of a photosensitizer for oral squamous cancer cells without swelling and inflammation. Therefore, photodin-based PDT is a suitable treatment for oral cavity carcinoma patients.