NOVELTY - Producing metal chalcogenide nanoparticles having number average molecular weight of 100 nm or less synthesized in a hydrophilic solvent, by modifying with a functional hydrophobic low-molecular compound, is new. The modified particles are extracted with hydrophobic solvent, and subsequently hydrophobic low-molecular compound is replaced with functional hydrophobic polymer.    USE - For forming polymer-modified metal chalcogenide nanoparticles (claimed) used for fluorescent substance for display, optoelectric transducer, light emitting diode, wavelength conversion material, ultraviolet-ray shielding material, dye-sensitized solar cell, fluorescent paint, fluorescent film, luminous paint, magnetic material, light-emission film, trace-component detection reagent, analytical reagent, drug delivery system, quantum transistor, quantum-dot laser, varistor and catalyst.    ADVANTAGE - The metal chalcogenide nanoparticles are easily and economically modified by a polymer. The aggregation of polymer-modified metal chalcogenide nanoparticles is prevented, and nanoparticles are stable for long period of time. The metal chalcogenide nanoparticles are easily separated and purified from unreacted raw material. The modified metal chalcogenide nanoparticles are excellent in electronic and quantum characteristics.    DETAILED DESCRIPTION - Producing metal chalcogenide nanoparticles having number average molecular weight of 100 nm or less synthesized in a hydrophilic solvent, by modifying with a functional hydrophobic low-molecular compound, is new. The modified particles are extracted with hydrophobic solvent, and subsequently hydrophobic low-molecular compound is replaced with functional hydrophobic polymer. The metal chalcogenide nanoparticles are obtained by mixing metallic compound and chalcogenization agent in hydrophilic solvent. The metallic compound is chosen from halide, organic-acid salt, nitrate, sulfate, perchlorate and/or acetylacetonate of metal. The chalcogenization agent is chosen from compounds such as MOH, M2S, MSH, H2S, M2Se, MSeH, H2Se, M2Te, MTeH, H2Te and thio urea.    M = alkali metal;    S = sulfur;    Se = selenium; and    Te = tellurium.    The metal in metal chalcogenide nanoparticles is chosen from zinc, titanium, zirconium, chromium, molybdenum, tungsten, manganese, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, copper, silver, cadmium, aluminum, gallium, indium, silicon, germanium, tin, lead, lanthanoid and/or actinoids. The functional hydrophobic low-molecular compound and functional hydrophobic polymer have functional group chosen from hydroxyl, carboxyl, mercapto, amino, carbamoyl, formyl, thioformyl, thiocarboxyl, dithiocarboxyl, trialkoxysilyl, alkali metal salt of hydroxyl, alkali metal salt of carboxyl, alkali metal salt of mercapto and/or alkali metal salt of dithiocarboxyl. The functional hydrophobic polymer is formed by polymerizing monomer chosen from (meth)acrylic ester, styrene, acrylonitrile and/or vinyl chloride, in presence of thiocarbonyl thio compound chain transfer agent.    An INDEPENDENT CLAIM is included for polymer-modified metal chalcogenide nanoparticles.