The present invention relates to an MRI contrast agent that includes zinc-containing water-soluble metal oxide nanoparticles and has an improved contrast effect. The zinc-containing water-soluble metal oxide nanoparticles are characterized by addition of zinc to a matrix comprising the metal oxide nanoparticles or by substitution of metal in the matrix, resulting in the improved contrast effect of MRI. In addition, the zinc-containing metal oxide nanoparticles of the present invention include the MRI contrast agent t having hybrid structures of &ldquozinc-containing metal oxide nanoparticle&mdashbiologically/chemically active material&rdquo in which the nanoparticle is conjugated with a bioactive material such as proteins, antibodies, and chemical materials.
