A method for producing single crystalline zinc oxide nanoparticles that is capable of mass production includes mixing, between processing surfaces which are disposed in a position facing each other so as to be able to approach and separate from each other and rotate relative to each other, a zinc oxide separating solvent prepared by homogeneously mixing an acidic substance with a solvent containing at least alcohol and a raw material solution obtained by mixing a zinc oxide nanoparticle raw material with a basic solvent or a raw material solution that is basic as a result of mixing and dissolving a zinc oxide nanoparticle raw material with and into a solvent, and discharging a mixed fluid in which zinc oxide nanoparticles have separated out from between the processing surfaces. The zinc oxide separating solvent and the raw material solution are mixed between the processing surfaces so that the mixed fluid becomes basic, and zinc oxide nanoparticles are generated by an acid-base reaction due to mixing of the acidic substance and the basic solvent.