A method for producing single crystalline zinc oxide nanoparticles in which the method for producing zinc oxide nanoparticles comprises: preparing a zinc oxide separating solvent by homogeneously mixing an acidic substance with a solvent containing at least alcohol; mixing, between processing surfaces which are disposed facing each other so as to be able to approach and separate from each other and at least one of the processing surfaces rotates relative to the other, the prepared zinc oxide separating solvent and a raw material solution that is obtained by mixing a zinc oxide nanoparticle raw material with a basic solvent, or 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, wherein 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 raw material solution, characterized in that the single crystal ratio of the generated zinc oxide nanoparticles is controlled by the preparation temperature of the zinc oxide separating solvent and/or wherein the single crystal ratio of the generated zinc oxide nanoparticles is controlled by the stirring energy that is input during preparation of the zinc oxide separating solvent, wherein the single crystal ratio = B A × 100, where A is the number of observed zinc oxide nanoparticles and B is the number of zinc oxide nanoparticles observed as single crystals therein. preparing a zinc oxide separating solvent by homogeneously mixing an acidic substance with a solvent containing at least alcohol; mixing, between processing surfaces which are disposed facing each other so as to be able to approach and separate from each other and at least one of the processing surfaces rotates relative to the other, the prepared zinc oxide separating solvent and a raw material solution that is obtained by mixing a zinc oxide nanoparticle raw material with a basic solvent, or 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, wherein 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 raw material solution, characterized in that the single crystal ratio of the generated zinc oxide nanoparticles is controlled by the preparation temperature of the zinc oxide separating solvent and/or wherein the single crystal ratio of the generated zinc oxide nanoparticles is controlled by the stirring energy that is input during preparation of the zinc oxide separating solvent, wherein the single crystal ratio = B A × 100, where A is the number of observed zinc oxide nanoparticles and B is the number of zinc oxide nanoparticles observed as single crystals therein.