A method of concentrating nanoparticles, having the steps of: adding and mixing an extraction solvent with a nanoparticles-dispersion liquid that nanoparticles are dispersed in a dispersion solvent, thereby concentrating and extracting the nanoparticles into a phase of the extraction solvent, and removing the dispersion solvent by filter-filtrating a liquid of concentrated extract, in which the extraction solvent is substantially incompatible with the dispersion solvent, and the extract solvent can form an interface after the extraction solvent is mixed with the dispersion solvent and left the mixture still; further a method of deaggregating aggregated nanoparticles, having the steps of: applying two or more ultrasonic waves different in frequency to a liquid containing aggregated nanoparticles, and thereby fining and dispersing the aggregated nanoparticles.