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A liquid chromatography-electrospray ionization tandem mass spectrometric method (LC-ESI-MS/MS) has been developed for the determination of benzidine (BZ) and 3, 3-dichlorobenzidine (DCBZ) from surface water. Parent ion of DCBZ gave strong signal with ESI by dissolving with 15mM ammonium formate, which is also used as mobile phase. Deuterated BZ (d8-BZ) was chosen as the internal standard (IS). BZ and DCBZ were extracted by solid-phase extraction on Oasis hydrophilic-lipophilic balance (HLB) from water at pH 8.0. The coefficients of variation of BZ and DCBZ were less than 13.1% and the detection limits were 0.004ngL(-1) for BZ and 0.7ngL(-1) for DCBZ using 0.5L surface water. The detection limit shows fair lower value than the water quality criteria for BZ and DCBZ established by the US EPA. When the proposed method was used to analyze the target compounds in sixteen surface water samples, BZ was detected in a concentration range of 0.15-2.33ngL(-1) in four of sixteen surface water samples