Abstract: The rnass spectra of 1-benzoyl-5-aryl-2-thiobiurets were reported. The mass spectral fragmentation was proposed on the basis of the high resolution mass spectrometry and the B/E linked scan spectra. The results show that 1-benzoyl-5-aryl-2-thiobiurets have strong molecular ion,the base peak is PhCO+,the cleavages take place at Q-position of carbonyl group;on the other hand,the bond between thiocarbonyl group and nitrogen atom can not break in the experimental condition.