Gold clusters with strong blue, green, and red fluorescence were synthesised with cysteine in one pot in acid solution. The yield of the blue and red fluorescent Au cluster could be made through adjusting the reactant ratio of cysteine/Au ions. Another Au cluster with strong green fluorescence located at 522 nm was also synthesised when strengthening the reductive ability of the cysteine through tuning the pH of the solution to 13, which gave evidence to the pH effect on the cluster formation. The disappeared -SH peak located at 2,544 cm<sup align="right"> −1 in the IR spectra verified that -SH group reduced the HAuCl<sub align="right"> 4 , and the gold clusters attached to the cysteine through the S-Au bond.