Abstract: Tetra-(p-hydroxylphenyl)porphyrin photosensitizer loaded with magnetic nanoparticles were prepared by means of emulsification and chemical co-precipitation.The morphology and size of the nanoparticles were analyzed by transmission electronic microscopy and X-ray diffraction,and their chemical structures were also analyzed by infrared spectroscopy.The magnetic response property was observed on a vibrating samples magnetometer.The content of photosensitizer was measured by UV-Vis spectrum.Their photodynamic activity against human Lovo colonic-carcinoma cell line in vitro was evaluated by MTT assay.The results reveal that the magnetic nanoparticles are regular sphere with a size of smaller than 50 nm,and the Fe₃O₄ particles were coated by the Dextran-40,the mass magnetic susceptibility was 68.27 emu/g,the content of porphyrin photosensitizer was 8.5%.The growth inhibitory rate of Volo cells was 81.85% after they were treated with magnetic nanoparticles,in which 1×10^-6 mol/L of tetra-(p-hydroxylphenyl)porphyrin was loaded,followed by irradiation of visible light for 30 min.