The present invention provides a silica nanoparticle for diagnostic imaging that is capable of use for X-ray CT, fluorescent imaging, or the like, and have high emission intensity. The present invention also provides a method for producing such a silica nanoparticle for diagnostic imaging. Also, a biosubstance labeling agent using the silica nanoparticle for diagnostic imaging is provided. The silica nanoparticle for diagnostic imaging of the present invention encapsulates an organic fluorescent dye and a metal complex, wherein a ligand of the metal complex form a covalent bond with constituent molecules of the silica nanoparticle.
