We report an easily scalable synthesis method for the preparation of cysteine-capped Cu≈10 clusters through the reduction of Cu(II) ions with NaBH4, using Cu5 clusters as catalysts. The presence of such catalytic clusters allows controlling the formation of the larger Cu≈10 clusters and prevents the production of copper oxides or Cu(I)-cysteine complexes, which are formed when Cu5 is absent or at lower concentrations, respectively. These results indicate that small catalytic clusters could be involved, as precursor species before the reduction step, in the different methods developed for the synthesis of clusters. The visible light-absorbing Cu≈10 clusters, obtained by the cluster-catalysed method, display high photocatalytic activities for the decomposition of methyl orange with visible light.