Abstract: Chloral represents one kind of common non-volatile chlorination by-product of the drained concentrated seawater from a seawater desalination plant, which has been proved to have mutagenicity.Therefore, it is necessary to establish a fast, sensitive and accurate method for detecting the concentration of chloral in concentrated seawater.Herein, a method is developed for this purpose by headspace and capillary GC with an electron capture detector(μECD).Determination parameters, such as headspace time, headspace temperature and seawater salinity are discussed in detail.The detection limits and correlation coefficient of method are respectively 0.006 μg/L and 0.9996.This method can be employed in the chloral concentration range of 0.05~20.0 μg/L.The relative standard deviation (RSD) is 0.51%~1.9%.Additionally, test for recovery is made by standard addition method, giving results in the range of 96.1%~113.9%.