As one of highly toxic and volatile chemicals,mustard gas has been widely used as a kind of chemical weapon in local wars and terrorist attacks.Realizing the rapid and accurate qualitative identification of mustard gas is the first step to prevent casualties from wars and terrorist attacks.The lab facilities based standard methods accompanied with tedious and time consuming operation are hardly satisfied the demand of emergence.Therefore,it is of great military significance to develop and establish a highly sensitive,accurate,simple and rapid detection technique towards on site detection of mustard gas.Taking the near single molecule level sensitivity and fingerprint resolution of surface enhanced Raman spectroscopy(SERS) herein,the feasibility of SERS for on site and quick detection of trace mustard gas was systematically explored,with 2-chloroethyl ethyl sulfide(2-CEES) as simulant and 50 nm gold nanoparticles colloid as SERS substrate,respectively.It was figured out that：(1) The SERS spectrum of trace 2 CEES showed obvious difference compared with the normal Raman spectrum of 2-CEES,as a result of the hydrolysis of 2-CEES and the accompanied formation of sulfonium;(2) Accordingly,the two characteristic Raman peaks located at 610 and 1 050 cm-1 of sulfonium could be used for the qualitative analysis of trace 2-CEES by SERS.Meanwhile,the lowest detectable concentration of 2-CEES was 10 μg/L.Furthermore,the reproducibility and stability were confirmed on both lab based bench top Raman instrument and portable one.The observation demonstrates that the SERS based strategy is very promising for the on site and rapid qualitative analysis of trace mustard gas in environmental waters.