Abstract: Chlorophenols in waste water sample were pre-derivatized in an alkaline solution containing dimethyl sulfoxide and benzyltriethylammonium chloride with iodomethane as derivatizing agent.Derivatives of chlorophenols,i.e.p-chlorophenol,2,4-dichlorophenol and 2,4,6-trichlorophenol,were separated and determined by gas chromatography with FID detector.Detection limits of the method obtained were 1.36 mg·L-1 for 4-chlorophenol,1.87 mg·L-1 for 2,4-dichlorophenol and 2.67 mg·L-1 for 2,4,6-trichlorophenol.Precision of measurements of peak area of derivatives of the 3 above mentioned chlorophenols was tested and values of RSD′s (n=5) obtained were 4.2%,3.4% and 5.1% respectively.