There is provided semiconductor nanoparticles which exhibit enhanced emission efficiency, excellent emission intensity, reduced variation range of emission characteristics among lots and among particles and are excellent in stability and reproducibility. There is further provided a fluorescent labeling agent and molecule/cell imaging method by use of the same. Semiconductor nanoparticles having an average particle size of 1 to 20 nm is disclosed, comprising a dopant of a heteroatom which is identical in valence electron configuration with a main component atom forming the semiconductor nanoparticles or an atomic pair of the heteroatom, and the dopant is distributed on or near a surface of the semiconductor nanoparticles.