We combine CdSe semiconductor nanocrystals (or quantum dots) and single-crystal ZnO nanowires to demonstrate a new type of quantumdot-sensitized solar cell. An array of ZnO nanowires was grown vertically from a fluorine-doped tin oxide conducting substrate. CdSe quantum dots, capped with mercaptopropionic acid, were attached to the surface of the nanowires. When illuminated with visible light, the excited CdSe quantum dots injected electrons across the quantum dol-nanowire interface. The morphology of the nanowires then provided the photoinjected electrons with a direct electrical pathway to the photoanode. With a liquid electrolyte as the hole transport medium, quantumdot-sensitized nanowire solar cells exhibited short-circuit currents ranging from 1 to 2 mA/cm 2 and open-circuit voltages of 0.5-0.6 V when illuminated with 100 mW/cm 2 simulated AM1.5 spectrum. Internal quantum efficiencies as high as 50-60% were also obtained.