Abstract: The residual octachloro-dipropylether (S-421) in tea was extracted with acetone and back-extracted with n-hexane.The S-421 in n-hexane was cleaned by liquid-liquid partition sulfonation with conc.H2SO4,and the sulfonated S-421 in n-hexane was used for GC determination.Measurements were made by ECD,and the method of external standards was use in determination.Tests of recovery were made by addition of standard S-421 to several portions of a tea sample at the concentration levels in the range of 0.005-0.05 mg·kg-1,and the values of recovery found were in the range of 85%-110%.Detection limit of the present method was 0.005 mg·kg-1.Precision of the method was tested by analyzing a same sample for 10 determinations,the values of RSD′s found were less than 10%.