We have investigated the sensitization of nanoporous titanium dioxide, zinc oxide, tin dioxide, niobium oxide, and tantalum oxide by quantum-sized cadmium sulfide, lead sulfide, silver sulfide, antimony sulfide, and bismuth sulfide. It was shown that the relative positions of the energetic levels at the interface between the quantum size particles and the oxide substrate can be optimized for an efficient charge separation by utilizing the size quantization effect and by varying the materials of the particles and the substrate. Photocurrent quantum yields of up to nearly 80% and open circuit voltages up to the 1-V range were measured. We showed that the photostability of the electrodes could be significantly enhanced by surface modification of the particles.