Preparation and processing of semiconductor nanoparticles by using reverse micellar systems were investigated. Size-controlled nanoparticles of metal sulfides such as CdS, ZnS and their composites, and metal oxides such as TiO2 were successfully prepared, and the formation mechanisms are discussed. The immobilization of these nanoparticles on polymer or silica supports through several new techniques including surface modification and in situ polymerization was investigated. The properties of the resulting semiconductor nanoparticles-polymer and -silica composites as photo-functional materials such as photocatalysts were elucidated.