Coupled TiO2-based semiconductor systems have attracted much interest because of synergistic effect on photocatalytic activity. Here, we prepared TiO2/Fe2O3 and TiO2/CuO bilayertype photocatalyst film and carried out the photodeposition of Ag to identify the reduction sites. We found that in the TiO2/Fe2O3 (CuO) boundary, deposition occurred preferentially on the side of TiO2. This phenomenon can be explained by semiconductor physics principles, not by the classical theory of interparticle electron transfer.