To provide a new liquid phase synthesis method for metal or metal- charcogen nanograins which are useful as a phase transition material, and to provide a high density an high sensitivity phase transition optical recording medium using the nanograins as a recording layer.

One or more kinds of metallic compounds and a reducing agent, or one or more kinds of metallic compounds and a charcogen compound are rapidly reacted by a stirring apparatus having high shearing force in an alcoholic solvent and/or water in which an adsorption group-containing low molecular dispersion agent and/or a polymer dispersion agent is dissolved, and further, refining is performed thereto by an ultrafiltration(UF) process. Further, these nanogranis are made into a colloid dispersion solution, and spin coating or web coating is applied thereto to made into a recording layer.