The magnetic photocatalysts can provide both a high specific surface area and an alternative for recovering used catalyst from treated water by the application of a magnetic field. In this study, the Fe3O4 nanoparticles were synthesized by co-precipitation. After chemical co-precipitation of ferric and ferrous solution under alkaline condition, the suspension of magnetite nanoparticles were then mixed with TEOT (Titanium (Ⅳ) ethoxide) for sol-gel coating. The separated MPCs (magnetic photocatalyst nanoparticle) were then dried and calcined in 400oC. Magnetic properties of MPCs were identified by superconducting quantum interference device magnetometer (SQUID). The bactericidal ability of synthesized MPCs was evaluated by counting the residual numbers of E. coli after irradiation under a light intensity of 1.0 mW/cm2 at 365 nm. The results show that the MPCs were both anatase and had good crystallinity with clear peaks and insignificant noises after calcination. The SQUID test also reveals that calcination only affects the magnetic susceptibility of the MPC nanoparticles slightly (< 8%). The bactericidal ability of the synthesized MPCs was compared with the commercial TiO2 nanoparticle DegussaTM P25; P25 provided a faster inactivation rate for E. coli in water than MPCs did at the same dosage. The calculated photocatalytic bactericidal rate by P25 is about 3.6 times faster than that by MPCs synthesized in this work. However, the bactericidal rate of magnetic TiO2 synthesized in this work was 5 times than that of other MPCs in the literature. The particles size and surface area of MPCs from this work were about 135 nm and 210 m2/g, respectively. The MPCs from this work have much smaller size and larger surface area; hence there are more active sites for bactericidal reaction.