Hg2+ is one of the most toxic heavy metal ions,which can cause air,soil,and water pollution,seriously damaging human health. Therefore,developing effective analytical methods to detect Hg2+ in environmental systems is particularly important. Fluorescent probes have been widely used to detect Hg2+ due to their advantages,such as high sensitivity,good selectivity,fast response time,and real-time online detection. In this paper,a novel “turn-on” fluorescent probe (2-(pyren-1-yl)-1,3-oxathiolane,POX) with 1,3-oxathiolane as receptor was designed and synthesized based on Hg2+-promoted deprotection reaction of thioacetal,and1H NMR,13C NMR,and HRMS characterized its structure. The selectivity,competitiveness,concentration titration,pH titration,time dependence,the limit of detection,and recognition mechanism of POX for the detection of Hg2+ in CH3CH2OH/H2O solution were investigated. The results showed that POX could quickly recognize Hg2+ in a wide pH range and exhibited high selectivity and sensitivity. Adding Hg2+ to the solution of POX resulted in a clear fluorescence emission peak at 386 nm,indicating that POX showed a remarkable “turn-on” fluorescence for Hg2+,and its recognition process was almost unaffected by other metal ions. Fluorescence titration experiments indicated that POX had a good linear response (R2=0.999 4) in the range of Hg2+ from 0~ 6.5 μmol·L-1,with a detection limit of 0.168 μmol·L-1. The RSD of POX for detecting Hg2+ in actual water samples was less than 2.92%. The simple synthesis,easy availability of raw materials,and wide pH applicability of POX suggested that itcould be used as a potential tool for the qualitative and quantitative detection of Hg2+ in the environment.