Provided is a method suitable for industrial-scale production of a dispersion in which nano-sized particles are dispersed. A method for producing a nanoparticle-in-oil dispersion in which fine particles made up of a solid component, an aqueous liquid component or a mixture thereof are dispersed in an oil phase, includes: (1) a step of preparing a W/O emulsion-type precursor in which an aqueous phase in the form of droplets of an aqueous solution having a water-soluble substance dissolved therein is dispersed in an oil phase； and (2) a step of boiling the aqueous phase of the W/O emulsion-type precursor, to obtain a nanoparticle-in-oil dispersion in which the fine particles are dispersed in the oil phase.
