A composite structure of magnetic nano photosensitizer TiO2/Fe3O4-SiO2 has been prepared by precipitation, Stöber and sol-gel methods, using ferrous sulfate, ferric chloride, tetraethyl orthosilicate and titanium tetrachloride as raw materials. Structure and property of the nano composite photosensitizer were characterized and analyzed by means of XRD, TEM, UV-Vis DRS and magnetic test. Methyl thiazolyl tetrazolium colorimetric method (MTT method) was used to investigate the killing effect of nano composite photosensitizer on A549 human lung cancer cells in vitro, and effects of different TiO2 loadings of TiO2/Fe3O4-SiO2 on the inhibition ratios of A549 human lung cancer cells were also studied. The characterization results showed that the nano composite photosensitizer had core shell structure and magnetism, had visible light absorption capability, and could respond to visible light at wavelengths above 400 nm. In vitro cytotoxicity assay results showed that when the illumination time was 150 min, mole fractions of inhibiting proliferation of A549 human lung cancer cells for the nano composite photosensitizer and pure TiO2 were 51% and 36% respectively, the nano composite photosensitizer with enhanced photodynamic activity. The optimum load for TiO2 was 30% in mass fraction.