Nanoparticles of Bi2Ti2O7 pyrochlore were synthesized by a coprecipitation method. They exhibit a high visible-light photoactivity for decolorization of a methyl-orange dye solution in the presence of a sacrificial agent, H2O2. The same pyrochlore system with an Ag co-catalyst showed even faster kinetics under only visible light and an unprecedentedly high photoactivity in the UV range.