Conversion of nitroarenes to aminoarenes has attracted great attention in pharmaceutical industry,agricultural production,environmental protection and chemical catalysis area.In this work,ficin capped gold nanoclusters(ficin@AuNCs) were prepared for the reduction of 4-nitrophenol to 4-aminophenol.The proposed catalyst was characterized by transmission electron microscopy,dynamic light scattering,fluorescence spectra and UV-Vis spectra.With NaBH4 as the reducing agent,the reduction reaction could carry out completely within 10 min at 25 ℃.Interestingly,the resultant catalyst exhibited size-related properties in the reduction,smaller ficin@AuNCs exhibited higher catalytic activity.Its present pseudo-first-order rate constant was found to be 2.95 × 10-3 s-1 and the catalytic activation energy was 27.7 kJ/mol.Moreover,ficin@AuNCs-based catalyst displayed good stability,heading to 4-nitrophenol conversion of 98.5%-100.0% after six consecutive cycles.It has shown a great potential in construction of unique catalysts based on AuNCs for reduction reaction.