Disclosed are water-soluble nanoparticles. The water-soluble nanoparticles are each surrounded by a multifunctional group ligand including an adhesive region, a cross linking region, and a reactive region. In the water-soluble nanoparticles, the cross-linking region of the multifunctional group ligand is cross-linked with another cross-linking region of a neighboring multifunctional group ligand. Furthermore, the present invention provides a method of producing water-soluble nanoparticles, which includes (1) synthesizing water-insoluble nanoparticles in an organic solvent, (2) dissolving the water insoluble nanoparticles in a first solvent and dissolving water-soluble multifunctional group ligands in a second solvent, (3) mixing the two solutions from the step (2) to substitute surfaces of the water-insoluble nanoparticles with the multifunctional group ligands and dissolving a mixture in an aqueous solution to conduct a separation process, and (4) cross-linking the substituted multifunctional group ligands with each other.