A novel photocatalyst was prepared by anchoring Au nanoparticles (NPs) onto one-dimensional potassium niobate (KNbO₃) nanowires. Photocatalytic activity towards rhodamine B degradation over Au/KNbO₃ appears to be much greater than that of KNbO₃ nanowires, nanorods and commercial Alfa Aesar. In terms of reaction rate constant (k), ultraviolet excitation (λ = 365 nm) is higher than that of visible-light (λ > 420 nm) and increasing the size of Au NPs from 5 to 10 nm significantly improves the reactivity. Notably, Au NPs with a size of ca. 10 nm supported on KNbO₃ nanowires display the greatest photoreactivity, with k exceeding that of commercial KNbO₃ by a factor of 15. The mechanism responsible for the enhancement of photocatalytic activity was discussed, highlighting the crucial role of surface plasmon resonance as well as interband transitions on Au NPs. This study is potentially applicable to a range of low-dimensional niobate-based nanostructures combined with Au and other plasmonic NPs with promising applications in photocatalysis and relevant areas.