For the property of persistent, bioaccumulation and genetic toxicity, perfluorooctanesulfonate (PFOS) is classified as a sort of persistent organic pollutants (POPs). It is significant to develop a novel assay for the determination of PFOS. In this work, we create a new colorimetric assay for PFOS in which the positively-charged gold nanoparticles (AuNPs) work as a nanoprobe. This method works on the aggregation of AuNPs induced by PFOS via electrostatic interaction. The stable monodisperse AuNPs coated by cysteamine present color of red wine and the addition of PFOS can make the monodispersed AuNPs aggregated resulting in the color change from wine red to reddish purple with a red-shift in ultraviolet-visible absorption spectrum. The experimental results show that AuNPs has a characteristic absorption peak (524 nm), as well as a wide absorption peak (650 nm) and the absorption signal intensity is proportional to the PFOS content in a range of 0.8～8.0 μmol·L-1. According to these, we developed a method based on ultraviolet-visible absorption and colorimetric to detect PFOS with the detection limit of 80 nmol·L-1. The scanning electron microscope (SEM) was investigated and the photos show that the stable AuNPs are made and the degree of AuNPs aggregation is related with PFOS concentration. The effect tests of coexisting substances in system show that common anions had less impact on the system and inorganic metal ions had some interference, which can be get rid of by cation exchange resin in real sample. This assay was applied to detect PFOS in tap water with a recovery range of 87.5%～118% and RSD≤4.4%. It is a novel application of AuNPs-based probe for PFOS detection. The proposed method has more advantages such as rapidity, low-cost and simplicity than conventional ones. In addition, it has the visual sensing function and the difference of color can be sensed by naked eyes directly, which produce ideas of real-time colorimetric strategies of nanoprobe application in environmental pollutant detection.