OEGylation of porphyrins via a disulfide linkage to form a novel class of dendritic porphyrin photosensitizers (PSs) is presented. These amphiphilic PSs possess precise molecular structures which could self-assemble into spherical aggregates in aqueous solutions. Their thermoresponsiveness was investigated using UV-Vis spectroscopy, and their reduction responsive properties were inspected using dynamic light scattering and TEM measurements. Moreover, the uptake of porphyrin-containing dendritic micelles by cells and release of reduction-sensitive PSs were investigated using flow cytometry and confocal laser scanning microscopy. The results showed that the cellular uptake of dendritic micelles was more than that of free porphyrin and the uptake process was time-dependent. Additionally, the phototoxicity of these dendritic PS micelles was investigated by MTT assay. It was found that dendritic micelles exhibited efficient phototoxicity to cancer cells while the free porphyrin had nearly no toxicity under light irradiation. All results indicate that these dendritic PSs are promising for photodynamic therapy.