Plasmon-induced photocatalysts hold great promise for solar energy conversion owing to their strong light-harvesting ability and tunable optical properties. However, the complex process of interfacial extraction of hot carriers and the roles of metal/semiconductor interfaces in plasmonic photocatalysts are still not clearly understood. Herein, the manipulation of the interface between a plasmon metal (Au) and a semiconductor (rutile TiO2) by introducing an interfacial metal oxide (Al2O3) is reported. The resulting Au/Al2O3/TiO2 exhibits remarkable enhancement in photocatalytic water oxidation activity compared with Au/TiO2, giving an apparent quantum efficiency exceeding 1.3% at 520 nm for photocatalytic water oxidation. Such an interfacial modulation approach significantly prolongs the lifetime of hot carriers in the Au/TiO2 system, which conclusively improves the utilization of hot carriers for plasmon-induced water oxidation reaction upon irradiation. This work emphasizes the essential role of the interfacial structure in plasmonic devices and provides an alternative method for designing efficient plasmonic photocatalysts for solar energy conversion.@en