The present invention relates to a 
manganese-containing 
metal oxide nanoparticle-based 
magnetic resonance imaging (MRI) contrast agent, which is characterized in that: The core of it comprises 1 to 1000 nm-sized 
manganese-containing 
metal oxide nanoparticles which include MnO a (0<a<5) or MnMbOe (wherein M is at least one 
metal atom selected from the group consisting of a Group 1 or 2 element such as Li, Na, Be, Ca, Ge, Mg, Ba, Sr and Ra, a Group 13 element such as Ga and In, a 
transition metal element such as Y, Ta, V, Cr, Co, Fe, Ni, Cu, Zn, Ag, Cd and Hg, and 
lanthanide or 
actinide group elements such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, 0<b<5 and 0<c<10); preferably MnM′dFeeOf (wherein M′ is at least one metal atom selected from the group consisting of a Group 1 or 2 element such as Li, Na, Be, Ca, Ge, Mg, Ba, Sr and Ra, a Group 13 element such as Ga and In, a 
transition metal element such as Y, Ta, V, Cr, Co, Fe, Ni, Cu, Zn, Ag, Cd and Hg, and 
lanthanide or 
actinide group elements such as La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb, 0<d<5, 0<e<5, and 0<f<15). In addition, the nanoparticles include water-soluble 
manganese-containing 
metal oxide nanoparticles which is characterized in that they are soluble in water themselves or stable in an aqueous media as being coated with a water-soluble ligand and they possess enhanced magnetic properties and MRI 
contrast effect. Also the 
water soluble manganese-containing 
metal oxide nanoparticles are coupled with an bioactive material such as chemical molecules or bio-functional molecules, and thus the nanoparticles can be used as an 
MRI contrast agent for target specificity and 
cell tracking.