Photoetching of single-crystal n-TiO2(rutile) in aqueous H2SO4 produced nanometer-sized rectangular holes, extending in the (001) direction and having selectively the (100) face at the walls. This led to an increase in water-oxidation activity. In the present study we have tried to photoeteh TiO2(rutile) nanoparticle in H2SO4. A number of minute holes were produced by photoetching of TiO2 particles on which Pt was pre-deposited, while no change occurred for TiO2 with no Pt. The result is understood by assuming that Pt promotes the charge separation in TiO2, which accelerates the photoetching.