A nanoparticle aqueous dispersion in which nanoparticles are dispersed in water is produced through a method including a step of freeze-drying a frozen sample of a liquid mixture of a first solution and a second solution and a step of dispersing the freeze-dried sample in water. In this method, the liquid mixture contains an active ingredient and an ointment base, the first solution includes contains an organic solvent as its solvent, and the second solution contains water as its solvent. The method, which is arranged as such, can provide an aqueous composition containing nanoparticles dispersed therein and usable stably as an aqueous dispersion preparation.
