A method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed for the simultaneous determination of the mercapturic acids derived from Benzene, 1,3-butadiene, acrolein and crotonaldehyde in human urine. The urine samples were cleaned up by an Isolute → ENV+ solid phase extraction column from Biotage Co. and separated by a C18 reversed-phase column, and then detected by tandem mass spectrometry in the mode of multiple reaction monitoring under electrospray ionization, using isotope-labeled analogs as internal standards. The analytes were S-phenylmercapturic acid (S-PMA), hydroxyl-butyl mercapturic acid (including monohydroxybutenyl-mercapturic acids MHBMA and dihydroxy-butyl-mercapturic acid DHBMA), 3-hydroxy-propyl mercapturic acid (3-HPMA) and 3-hydroxy-1-methylpropyl mercapturic acid (3-HMPMA). These calibration curves all showed good linearity. The detection limits of the developed method ranged from 0.8 to 4.2 ng/ml, recoveries were between 97.17% and 112.49% and relative standard deviations for six separated determinations were between 1.02% and 9.03%. With this method, the mercapturic acids in the urine samples of smokers and non-smokers were determined and analyzed.