The catalytic activity of one-pot synthesis gold clusters protected by L-glutathione is studied. Different sizes gold clusters Au₂₅(SG)₁₈ and in average 1.5 nm and 3 nm Au_n(SG)_m are deposited over aluminium dioxide (Al₂O₃ Puralox SCCa-190HPV). The synthesized clusters on alumina (1% Au_n(SG)_m/Al₂O₃) were tested as new catalysts in reduction of 4-nitrophenol (4-NP) in presence of aqueous NaBH₄. The results showed that the 1% Au₂₅(SG)₁₈/Al₂O₃ catalyst exhibited the best catalytic performance in the reduction of 4-NP into 4-aminophenol (4-AP) and revealed 100% conversion following 2 min stirring at room temperature. The catalyst weight was used in this reaction 0.3 g/L. The particles sizes and optical properties of synthesized clusters were investigated by transmission electron microscopy and UV–vis spectroscopy, respectively. The catalytic reduction reaction of 4-NP were followed by UV–vis spectroscopy. N₂ sorptiometry were used for the characterization of surface morphology, specific surface area S_BET, pore volume and average pore diameter for synthesized clusters on alumina. The extreme catalytic activity of the small gold clusters attribute to their electronic properties. The partial positive charges of the surface gold atoms in the Au₂₅(SR)₁₈ clusters should facilitate the electron transfer from the negatively charged BH₄⁻ to 4-NP.