The invention provides a semiconductor nanoparticle comprising a semiconductor nanoparticle core on the surface of which electron-releasing groups are arranged, the semiconductor nanoparticle having a fluorescent property and water-solubility. The invention also provides a water-soluble semiconductor nanoparticle with an excellent fluorescent property that can be easily prepared by adding a surface-treating material for providing a semiconductor nanoparticle with one or more kinds of electron-releasing groups, and arranging the electron-releasing groups on the surface of the semiconductor nanoparticle core.