Light-driven proton-coupled electron transfer (PCET) reactions on nanoplasmonics would bring temporal control of their reactive pathways, in particular, prolong their charge separation state. Using a silver nano-hybrid plasmonic structure, we observed that optical excitation of Ag-localized surface plasmon instigated electron injection into TiO2 conduction band and oxidation of isopropanol alcoholic functionality. Femtosecond transient infrared absorption studies show that electron transfer from Ag to TiO2 occurs in ca. 650 fs, while IPA molecules near the Ag surface undergo an ultrafast bidirectional PCET step within 400 fs. Our work demonstrates that ultrafast PCET reaction plays a determinant role in prolonging charge separation state, providing an innovative strategy for visible-light photocatalysis with plasmonic nanostructures.