This study examined the optical properties of an oxidized form of maghemite (γ-Fe(2)O(3)) nanoparticles and their protective effects against the photoaging of human skin fibroblasts irradiated with ultraviolet (UV) light. Nanoparticles with diameters ranging from 8.7 to 12 nm were prepared using a chemical co-precipitation method. The nanoparticles were coated with two surfactants to obtain a water-based product. The onset of the absorption of the γ-Fe(2)O(3) nanoparticles in the UV-visible absorption spectra increased with increasing particle size. The γ-Fe(2)O(3) nanoparticles significantly inhibited the production of matrix metalloproteinase-1 in human skin fibroblast HS 68 cells by 60% compared with the UV-irradiated control. These results suggest that γ-Fe(2)O(3) nanoparticles have photoprotective properties, and have potential use as an agent against photoaging.