The limit of the detection (LOD) of this Hg2+ detection system is 0.1 M by the naked eyes and 5.0 nM by UV–vis spectroscopy, which is lower than the mercury toxic level (10 nM)defined by the US Environmental Protection Agency and reaches the sanitary standard of drinking water of China. It’s a good linear relationship (R2= 0.9919) between A520/A680 and Hg2+ concentration from 0.01 M to 2.0 M, which is used for the quantitativeassay of Hg2+. This detection system also exhibits satisfying performances in real water samples. These results indicate that our AuNPs-based detection system is applicable for rapid colorimetric detection of Hg2+with excellent selectivity and high sensitivity in complicated environmental samples.