A simple and sensitive aptamer-based colorimetric detection of 17β-estradiol was developed using unmodified gold nanoparticles（AuNPs） as colorimetric probe.It is based on the fact that aptamer can be absorbed onto the surface of AuNPs by electrostatic interaction and then the adsorbed aptamer can protect AuNPs against salt-induced aggregation.Upon the addition of 17β-estradiol,the aptamer combined with its target and dissociated from the surface of AuNPs,thus causing AuNPs aggregation under high-salt conditions and the color of such AuNPs solution changed from red to blue.In a typical experiment,the 50 μL 1 μmol/L 17β-estradiol’s aptamer solution and 50 μL AuNPs were added into microplate well and incubated for 5 min.Then 50 μL different concentrations of 17β-estradiol was added to increase a volume up to 150 μL,homogenized and allowed to stand for 5 min.Subsequently,10 μL 2 mol/L NaCl was transferred to the solution to give a final volume of 160 μL and mixed thoroughly.After the solution was equilibrated for 5 min,the UV absorbance spectrum of the solution in the range of 450-750 nm was obtained by UV/Vis spectroscopy.The results showed that,with increase of 17β-estradiol concentration,the color of the solution changed from red to blue and the ratio of OD620/OD520 was increased.As low as 10 ng/mL 17β-estradiol could be detected.In order to determine the specificity of this method,the sensing platform against several non-specific targets was tested.The structural analogues such as estriol,estrone,19-nortestosterone could also cause the color of the solution changing from red to blue with high concentration.while in the presence of other estrogen like matters（such as diethylstilbestrol,bisphenol A and the solvent of methanol）,the solution would still keep red even under high concentration.The results showed that the developed method has high specificity.All of these results illustrated that the method could be readily extended toward the on-site monitoring of 17β-estradiol in environmental matrices.