Biosorption has been shown to be an eco-friendly approach to remove heavy metal ions. In this study, the photosynthetic bacteria Rhodobacter capsulatus was screened and found to have strong ability to adsorb Au(III). The maximum specific uptake of living cells was over 92.43 mg HAuCl4/g dry weight of cell in the logarithmic phase. Biosorpion ability would be enhanced by an acidic environment. As the main cations, during biosorption the quantity of Mg2+ exchanged was more than Na+. Biosorbed Au(III) could be reduced by carotenoid and enzymes embedded and/or excreted by R. capsulatus, which might be the mechanism of photosynthtic bacteria metal tolerance.