Metal–semiconductor nanocomposites have been widely employed for designing efficient optoelectronic devices and catalysts. The performance of such nanocomposites is significantly influenced by both the method of preparation and the electronic and morphological structures of metals and semiconductors. Here, we have synthesized novel nanocomposites containing plate-like anatase TiO2 mesocrystal superstructures and noble metal (Au, Pt) nanoparticles. These metal nanoparticles were preferentially photodeposited on the edge of TiO2 mesocrystals. The electron transport and photocatalytic properties of the novel nanocomposites were subsequently studied. Single-molecule fluorescence spectroscopy measurements on a single particle directly revealed that most of the photogenerated electrons could migrate from the dominant surface to the edge of the TiO2 mesocrystal with the reduction reactions mainly occurring at its lateral surfaces containing {101} facets. The loading of metal nanoparticles on the superstructure o...