The development of high-performance visible-light-driven photocatalysts is attractive for the simultaneous achievement of sustainable hydrogen production and waste-water treatment in an economical and large-scale manner. An ordered mesoporous composite of quantum-sized CdS (q-CdS)/Ta2O5 with enhanced interfacial charge transfer was prepared by evaporation-induced self-assembly in the presence of a triblock-copolymer surfactant followed by ion-exchange treatment. The incorporation of cubic CdS into an amorphous Ta2O5 framework effectively extended its spectroscopic response from the ultraviolet into the visible region. The quantum-confinement effect of CdS nanoparticles (3–4 nm) afforded an increased potential gradient between q-CdS and Ta2O5, thereby accelerating the transfer of photogenerated electrons from q-CdS to Ta2O5 and suppressing the recombination of charge carriers. Owing to this increased potential gradient and the large specific surface area, as well as the strong adsorption capability towards methylene blue (MB), the as-prepared ordered mesoporous photocatalyst exhibited significantly enhanced visible-light-driven photocatalytic activity and long-term stability for hydrogen evolution from simulant waste water that contained MB in the absence of any co-catalysts. These results may have applications in the sustainable production of hydrogen energy and in environmental remediation.