Provided are: novel rutile titanium dioxide nanoparticles each having a high photocatalytic activity; a photocatalyst including the rutile titanium dioxide nanoparticles; and a method for oxidizing an organic compound using the photocatalyst. The rutile titanium dioxide nanoparticles each have an exposed crystal face (001). The rutile titanium oxide nanoparticles may be produced by subjecting a titanium compound to a hydrothermal treatment in an aqueous medium in the presence of a hydrophilic polymer. A polyvinylpyrrolidone, for example, is used as the hydrophilic polymer. An organic compound having an oxidizable moiety can be oxidized with molecular oxygen or a peroxide under photoirradiation in the presence of the photocatalyst including the rutile titanium oxide nanoparticles.