Abstract: OBJECTIVE Introduce the studies progress on the target of photodynamic therapy (PDT) with porphyrin derivatives as photosensitizers. METHODS This article discussed the evidences of mitochondria as the target site in PDT with three lines of data: the distribution characters of porphyrin derivatives as the photosensitizers in the cell; reactive oxygen species, the mitochondrial pathway for cell apoptosis in PDT. RESULTS Porphyrin derivatives as the most common photosensitizers could selectively concentrated at the target cell to produce reactive oxygen species, which lead to the destruction of target cells. CONCLUSION About where is the PDT target site in the cell, there is no concensus in the early studies, but increasing studies found that mitochondria may be the main target in PDT.