This invention provides a Fe3O4/TiO2 composite nano-particle, its preparation and application in the magnetic resonance imaging (MRI) contrast agent, wherein the preparation of Fe3O4/TiO2 composite nano-particles has the followings steps: trivalent iron compounds and bivalent iron compounds are dissolved into a reducing acid water solution, and then added with tetravalent titanium salt solution to obtain the Fe3O4/TiO2 composite nano-particle sol. The Fe3O4/TiO2 composite nano-particles prepared by the method in the invention have the properties of superparamagnetism and photocatalytic activity and can be applied to MRI contrast agents.
