Abstract: A method for the determination of four haloacetic acids including dichloroacetic acid, trichloroacetic acid, monoiodoacetic acid and diiodoacetic acid in drinking water by liquid chromatography-tandem mass spectrometry was proposed. The filtered water sample (0.5 mL) was taken and mixed with 0.5 mL of acetonitrile. Torus DEA column was used as stationary phase, and isocratic elution was performed by the mixed solution composed of 2.0% (volume fraction) ammonia solution containing 1.0 mmol·L^-1 ammonium acetate and acetonitrile at volume ratio of 10∶90 as mobile phase. Four separated targets were scanned by electrospray ion source with negative ion mode, detected by multi-reaction monitoring mode, and quantified by external standard method. As shown by the results, linear relationships between the mass concentrations of four haloacetic acids and the peak areas of quantitative ions were kept in the range of 5-100 μg·L^-1, with detection limits (3S/N) in the range of 0.3-3.0 μg·L^-1. Test for recovery was made on the tap water sample at 3 concentration levels by standard addition method, giving results in the range of 70.1%-114%, and RSDs (n=6) of the determined values ranged from 0.90% to 5.8%. The method was used to analyze 10 samples of peripheral water, in which monoiodoacetic acid, diiodoacetic acid and trichloroacetic acid were not detected, with the detected amount of dichloroacetic acid in the range of 2.0-4.4 μg·L^-1 in 8 samples.