To develop an gas chromatography-electrophoretic capture detection (GC-ECD)method for determining dimethyl sulphate (DMS) in environmental samples.The environmental samples were dissolved with acetone and the DMS was reacted with KI. The reaction product of methyl iodide was extracted with Hexane and determined by GC-ECD, with HP-5 (30.0 m x 0.32 mm x 0.25 microm) as column, high purity nitrogen as carries, 60 degrees C for column temperature and 240 degrees C for ECD and injector temperature, and 5:1 for split ratio.The linear range appeared from 0.05 microg/mL to 2.0 microg/mL. The detection limit was 0.0011 microg/mL. The precision [measured by relative standard deviation (RSD)] of peak area and reserved time for the standard solution was 4.95% and 0.15% respectively for intra-day detections, and 5.99% and 0.83% respectively for inter-day detections. Satisfactory results were obtained for the analysis of environmental samples. The RSD for the water and soil samples were 9.6% and 7.5% respectively and the recoveries were 76.0%-85.0% and 82.0%-110.0% respectively.The method was simple, accurate, sensitive and applicable for DMS analysis in environmental samples.