Non-noble metal copper (Cu) nanoparticles (NPs) with controlled size and surface coverage are decorated on silicon nanowire arrays (SiNWAs) by a simple galvanic displacement reaction. Using the combined efforts of all these approaches, SiNWAs-supported Cu NPs (SiNWAs–Cu) exhibit excellent and stable activity for the catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) by sodium borohydride (NaBH₄) in an aqueous solution, which can be recycled for five successive cycles of the reaction with a conversion efficiency of more than 95%. This novel catalyst also shows excellent catalytic performance for the degradation of other organic dyes, such as methylene blue (MB) and rhodamine B (RhB). Additionally, we demonstrate that the catalytic activity of SiNWAs–Cu is comparable to other SiNWAs-supported noble metal NPs (i.e., Ag and Au). Furthermore, SiNWAs as powerful substrates can be reused for decorating with Cu NPs after dilute HNO₃ treatment. SiNWAs–Cu is particularly attractive as a catalyst, although Cu is orders of magnitude cheaper than any noble metals, its catalytic performance is comparable to other noble metals. So SiNWAs–Cu is thus expected to have the potential as a highly efficient, cost-effective and eco-friendly reusable catalyst to replace noble metals for certain catalytic applications.