PROBLEM TO BE SOLVED: To stably classify nanoparticles almost in a monodispersion state according to the size from a sol containing fine particles prepared as micelles without depending on the sol liquid or micelle substances.
SOLUTION: A sol containing nanosize fine particles prepared as micelles is mixed with a surfactant and org. solvent, and is left to stand for a while to be separated into an org. solvent emulsion phase and water phase. By successively subjecting the water phase separated to the same process above described, nanosize fine particles in a monodispersion state are collected in each org. solvent emulsion phase.